Oil Hydraulics & Pneumatics Lab Manual: Experiments & Circuits

▼▼
Scroll Down to View your Downloaded File! ▼▼
Disclaimer
Please note none of the content or study material in this document or content in this file is prepared or
owned by AceTechie.com. This content is shared by our student partners and we do not hold any
copyright on this content.
Please let us know if the content in this file infringes any of your copyright by writing to us at:
[email protected] and we will take appropriate action.
B.E. - SEMESTER - VII
OIL HYDRAULICS AND PNEUMATICS
INDEX
Sr.
No.
Title of Experiments
1
To study about symbols hydraulic and
pneumatic component used in hydraulic
and pneumatic circuits.
2
To study about basics of hydraulic
system and its components
3
To study about hydraulic fluids and its
properties
4
To study about hydraulic pumps and
actuators
5
To study about different types of control
valves used in hydraulic system
6
To study about basic and industrial
hydraulic circuits
7
To study about basic pneumatic system
and its component
8
To study about pneumatic compressors
and its characteristics
9
To study about special valves used in
pneumatic circuit
10
To study about different basic and
industrial pneumatic circuits
11
To study about automation in hydraulic
and pneumatic systems
12
Case study
e
T
Page
no.
A
Ending
date
Sign
m
o
.c
ie
h
c
e
c
Starting
date
Remarks
Hydraulic and Pneumatic symbols
EXPERIMENT – 1
AIM – To study about symbols hydraulic and pneumatic component used in hydraulic and
pneumatic circuits.
Lines
Continuous line (for) flow line
Dashed line (for) pilot, drain
Envelope (for) long and short dashes
around two or more component
symbols.
m
Circular
o
Large circle - pump, motor
.c
Small circle - Measuring devices
Semi-circle - rotary actuator
ie
h
Square
c
e
-One square - pressure control
function
-Two or three adjacent squares directional control
e
T
Diamond
Diamond - Fluid conditioner
(filter, separator, lubricator, heat
exchanger)
Miscellaneous Symbols
c
Spring
A
Flow Restriction
Triangle
Solid - Direction of Hydraulic
Fluid Flow
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.1
Hydraulic and Pneumatic symbols
Open - Direction of Pneumatic
flow
Pumps and Compressors
Fixed Displacement hydraulic pump symbols
Unidirectional
Bidirectional
Unidirectional
Bidirectional
m
Compressor symbol
Motors
.c
Fixed displacement hydraulic motor symbol
Unidirectional
Bidirectional
c
e
o
ie
h
Variable displacement hydraulic motor symbol
Unidirectional
Bidirectional
e
T
c
Pneumatic motor symbol
A
Unidirectional
Bidirectional
Rotary Actuator symbol
Hydraulic
Pneumatic
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.2
Hydraulic and Pneumatic symbols
Cylinders
Single acting cylinder symbols
Returned by external force
Returned by spring or extended by spring
force
Double acting cylinder symbols
Single piston rod (fluid required to
extend and retract)
m
Double ended piston rod
o
Cylinders with cushions symbols
.c
Single fixed cushion
Double fixed cushion
Single adjustable cushion
Double adjustable cushion
c
e
ie
h
Directional Control Valve symbols
T
Directional control valve (2 ports / 2 positions)
e
Normally closed directional control valve
with 2 ports and 2 finite positions
c
A
Normally open directional control valve
with 2 ports and 2 finite positions
Directional control valve (3 ports / 2 positions)
Normally closed directional control valve
with 3 ports and 2 finite positions
Normally open directional control valve
with 3 ports and 2 finite positions
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.3
Hydraulic and Pneumatic symbols
Directional control valve (4 ports / 2 positions)
Directional control valve with 4 ports
and 2 finite positions
Directional control valve (4 ports / 3 positions)
Directional control valve with 4 ports
and 3 finite positions (center position
can have various flow paths)
Directional control valve (5 ports / 2 positions) normally a pneumatic valve
Directional control valve with 5 ports
and 2 finite positions
Directional control valve (5 ports / 3 positions) Normally a pneumatic valve
Directional control valve with 5 ports
and 3 finite positions
.c
Manual Control
General symbol of a valve's manual
operator (without showing the control
type)
Pushbutton
Lever
Foot pedal
e
T
c
e
m
o
Control Method Operator symbols for valves
ie
h
Mechanical Valve Control
c
A
Plunger or tracer
Spring (used on one side of a valve to
hold it in the normally open or normally
closed state)
Roller
Roller (one direction only)
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.4
Hydraulic and Pneumatic symbols
Electrical/Solenoid Valve Control
Solenoid (the one side's winding shown)
Pilot Operation
(uses pressure to actuate valve)
Pneumatic actuated pilot
Hydraulic actuated pilot
Pilot operated two-stage valve (uses a second lesser force to actuate the pilot
actuation of the valve)
Pneumatic: Solenoid first stage
m
Pneumatic: Air pilot second stage
o
.c
Hydraulic: Solenoid first stage
Hydraulic: Hydraulic pilot second stage
ie
h
Check valves, Shuttle valves, Rapid Exhaust valves
Check valve symbol-free flow one
direction, blocked flow in other direction
c
e
Pilot operated check valve symbol, pilot
to close
e
T
Pilot operated check valve symbol, pilot
to open
c
A
Shuttle valve
Rapid exhaust valve/Pneumatic
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.5
Hydraulic and Pneumatic symbols
Pressure Control Valves
Pressure Relief Valve (safety valve) normally closed
Line pressure is limited to the setting of
the valve, secondary part is directed to
tank.
Proportional Pressure Relief Valve
Line pressure is limited to and
proportional to an electronic signal
Sequence Valve
When the line pressure reaches the setting
of the valve, valve opens permitting flow
to the secondary port. The pilot must be
externally drained to tank.
m
.c
Pressure Reducing valve (Hydraulic Pressure Regulator)
Pressure downstream of valve is
limited to the setting of the valve
o
ie
h
Flow Control Valves
Throttle valve
Adjustable output flow
Flow Control valves
e
T
c
e
c
Flow control valve with fixed
output (variations in inlet pressure do not
affect rate of flow
A
Flow control valve with fixed output and
relief port to reservoir with relief for
excess flow (variations in inlet pressure
do not affect rate of flow)
Flow control valve with variable output
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.6
▼▼
Scroll Down to View your Downloaded File! ▼▼
Hydraulic and Pneumatic symbols
Flow control valve with fixed orifice
Flow control valve with metered flow
toward right free flow to left
Flow control valve with pressure
compensated flow control fixed output
flow regardless of load
Flow control valve with pressure and
temperature compensated
Shut-Off Valve
Shut-Off Valve Simplified symbol
m
Accumulators
o
Accumulator symbol (Stores Pressure)
ie
h
Reservoir (Tank)
Reservoir symbol (Holds Fluid medium of
your system)
c
e
.c
Filters, Water Traps, Lubricators and Miscellaneous Apparatus
Filter or Strainer
e
T
c
Water Trap
A
Filter with water trap
Air Dryer
Lubricator
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.7
Hydraulic and Pneumatic symbols
Conditioning unit (FRL, Pressure
Regulator)
Heat Exchangers
m
o
.c
e
T
c
e
ie
h
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 1.8
Basics of Hydraulic System
EXPERIMENT – 2
AIM – To study about basics of hydraulic system and its components
2.1 INTRODUCTION
In the industry we use three methods for transmitting power from one point to another.
Mechanical transmission is through shafts, gears, chains, belts, etc. Electrical transmission is
through wires, transformers, etc. Fluid power is through liquids or gas in a confined space. In
this chapter, we shall discuss a structure of hydraulic systems and pneumatic systems. We
will also discuss the advantages and disadvantages and compare hydraulic, pneumatic,
electrical and mechanical systems.
Table 2.1 - Applications of fluid power
Agriculture
o
.c
Automation
Automobiles
Aviation
Construction
industry/equipment
e
c
A
Defense
Entertainment
Fabrication industry
Food and beverage
Foundry
m
Tractors; farm equipment such as
mowers, ploughs,
chemical and water sprayers, fertilizer
spreaders, harvesters
Automated transfer lines, robotics
Power steering, power brakes,
suspension systems,
hydrostatic transmission
Fluid power equipment such as
landing wheels in aircraft.
Helicopters, aircraft trolleys, aircraft
test beds, luggage loading and
unloading systems, ailerons, aircraft
servicing, flight simulators
For metering and mixing of concrete
rudders, excavators,
lifts, bucket loaders, crawlers, posthole diggers, road graders, road
cleaners, road maintenance vehicles,
tippers
Missile-launching systems, navigation
controls
Amusement park entertainment rides
such as roller coasters
Hand tools such as pneumatic drills,
grinders, borers,
riveting machines, nut runners
All types of food processing
equipment, wrapping, bottling,
Full and semi-automatic molding
machines, tilting of furnaces, diecasting machines
T
c
e
ie
h
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.1
Basics of Hydraulic System
Glass industry
Instrumentation
Jigs and fixtures
Machine tools
Materials handling
Medical
m
Movies
o
Mining
Newspapers and periodicals
Oil industry
Paper and packaging
Pharmaceuticals
Plastic industry
Press tools
Vacuum suction cups for handling
Used to create/operate complex
instruments in space
rockets, gas turbines, nuclear power
plants, industrial labs
Work holding devices, clamps,
stoppers, indexers
Automated machine tools,
numerically controlled(NC)
machine tools
Jacks, hoists, cranes, forklifts,
conveyor systems
Medical equipment such as breathing
assistors, heart assist
devices, cardiac compression
machines, dental drives and human
patient simulator
Special-effect equipment use fluid
power; movies such as
Jurassic park, Jaws, Anaconda,
Titanic
Rock drills, excavating equipment,
ore conveyors, loaders
Edge trimming, stapling, pressing,
bundle wrapping
Off-shore oil rigs
Process control systems, specialpurpose machines for
rolling and packing
Process control systems such as bottle
filling, tablet placement, packaging
Automatic injection molding
machines, raw material
feeding, jaw closing, movement of
slides of blow molder
Heavy duty presses for bulk metal
formation such as sheet
metal, forging, bending, punching,
etc.
For paper feeding, packaging
Fluid power operated robots,
pneumatic systems
Stabilizing systems, unloading and
loading unit, gyroscopic
instruments, movement of flat forms,
lifters, subsea inspection equipment
Web tensioning devices, trolleys,
process controllers
Hydraulic elevators, winches,
c
e
A
Printing industry
Robots
Ships
Textiles
Transportation
T
.c
c
e
ie
h
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.2
Basics of Hydraulic System
overhead trams
Submarines, under sea research
vehicles, marine drives and control of
ships
Tree shearers, handling huge logs,
feeding clamping and
saw operations
Under sea
Wood working
2.2 CLASSIFICATION OF FLUID POWER SYSTEMS
The fluid power system can be categorized as follows:
1. Based on the control system

Open-loop system: There is no feedback in the open system and performance is
based on the characteristics of the individual components of the system. The openloop system is not accurate and error can be reduced by proper calibration and
control.

Closed-loop system: This system uses feedback. The output of the system is fed back
to a comparator by a measuring element. The comparator compares the actual output
to the desired output and gives an error signal to the control element. The error is used
to change the actual output and bring it closer to the desired value. A simple closedloop system uses servo valves and an advanced system uses digital electronics.
m
o
.c
2. Based on the type of control

ie
h
Fluid logic control: This type of system is controlled by hydraulic oil or air. The
system employs fluid logic devices such as AND, NAND, OR, NOR, etc. Two types
of fluid logic systems are available:
c
e
(a) Moving part logic (MPL)
(b) Fluidics

T
Electrical control: This type of system is controlled by electrical devices. Four basic
electrical devices are used for controlling the fluid power systems: switches, relays,
timers and solenoids. These devices help to control the starting, stopping, sequencing,
speed, positioning, timing and reversing of actuating cylinders and fluid motors.
Electrical control and fluid power work well together where remote control is
essential.
e
c

A
Electronic control: This type of system is controlled by microelectronic devices. The
electronic brain is used to control the fluid power muscles for doing work. This
system uses the most advanced type of electronic hardware including programmable
logic control (PLC) or microprocessor (P). In the electrical control, a change in
system operation results in a cumbersome process of redoing hardware connections.
The difficulty is overcome by programmable electronic control. The program can be
modified or a new program can be fed to meet the change of operations. A number of
such programs can be stored in these devices, which makes the systems more flexible.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.3
Basics of Hydraulic System
2.3 HYDROSTATIC AND HYDRODYNAMIC SYSTEMS
− A hydrostatic system uses fluid pressure to transmit power. Hydrostatics deals with the
mechanics of still fluids and uses the theory of equilibrium conditions in fluid. The system
creates high pressure, and through a transmission line and a control element, this pressure
drives an actuator (linear or rotational).
− The pump used in hydrostatic systems is a positive displacement pump. The relative spatial
position of this pump is arbitrary but should not be very large due to losses (must be less
than 50 m). An example of pure hydrostatics is the transfer of force in hydraulics.
− Hydrodynamic systems use fluid motion to transmit power. Power is transmitted by the
kinetic energy of the fluid. Hydrodynamics deals with the mechanics of moving fluid and
uses flow theory. The pump used in hydrodynamic systems is a non-positive displacement
pump.
− The relative spatial position of the prime mover (e.g., turbine) is fixed. An example of pure
hydrodynamics is the conversion of flow energy in turbines in hydroelectric power plants.
m
o
− In oil hydraulics, we deal mostly with the fluid working in a confined system, that is, a
hydrostatic system.
2.4 GENERAL LAYOUT OF HYDRAULIC SYSTEM
2.4.1 Components of Hydraulic System
.c
ie
h
− Basic hydraulic system has the following components:
1) Oil reservoir
2) Rotary pump
3) Pressure relief valve
6) Double acting cylinder
5) Flow control valve
7) Pressure gauge
1) Oil Reservoir
e
c
e
4) Direction control valve
T
8) Filter
− Main function of "oil reservoir" is to store sufficient amount of hydraulic oil in the system.
c
− Apart from this, it has other important functions such as:
A
(a) To cool the hot return oil.
(b) To settle down the contaminants.
(c) To remove air bubbles.
(d) To separate water from the oil etc.
2) Rotary pump
− The function of rotary pump is to pump hydraulic oil to the hydraulic circuit
− It converts the mechanical energy (rotation of shaft) into hydraulic energy
− Rotary pump is a positive displacement pump. It can deliver constant flow even at high
pressure
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.4
Basics of Hydraulic System
3) Pressure relief valve
− It is an important component which is required for every positive displacement pump
− This valve is connected at the outlet of pump. Its main function is to release the oil back
tank when the pressure increases beyond pre-set value.
m
o
.c
c
e
ie
h
Figure 2.1 - Layout of general hydraulic system
4) Direction control valve
T
− It controls the direction of flow of oil, by which it performs extension and retraction of
e
actuator
c
5) Flow control valve
− It Controls the rate of flow of oil by which speed of extension or retraction of actuator is
A
controlled.
6) Actuator
− Actuator produces work. There are two types, linear actuator and rotary actuator
− Linear actuator is called cylinder, rotary actuator is called motor.
− Double acting cylinder develops force and motion. It converts hydraulic energy in to
mechanical energy
Force developed = Pressure of oil x Area of piston
7) Pressure gauge
− It is an important component of hydraulic system.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.5
Basics of Hydraulic System
− It shows the pressure reading.
− Pressure settings are made by looking to the pressure gauge.
− Without pressure gauge, it is not possible to make the pressure relief valve setting,
unloading valve settings etc.
8) Filter
− Its main function is to remove suspended solid contaminates from the oil and to provide
clean hydraulic oil to the system.
2.5 BASIC ELECTRICAL DEVICES
− Seven basic electrical devices commonly used in the control of fluid power systems are:
1. Manually actuated push button switches
2. Limit switches
3. Pressure switches
m
4. Solenoids
o
5. Relays
6. Timers
.c
7. Temperature switches
− Other devices used in electro pneumatics are
1. Proximity sensors
2. Electric counters
2.5.1 Push button switches
c
e
ie
h
− A push button is a switch used to close or open an electric control circuit. They are
primarily used for starting and stopping of operation of machinery.
T
− They also provide manual override when the emergency arises. Push button switches are
actuated by pushing the actuator into the housing. This causes set of contacts to open or close.
e
c
− Push buttons are of two types
i) Momentary push button
A
ii) Maintained contact or detent push button
− Momentary push buttons return to their unactuated position when they are released.
Maintained (or mechanically latched) push buttons has a latching mechanism to hold it in
the selected position.
− The contact of the push buttons, distinguished according to their functions,
i) Normally open (NO) type
ii) Normally closed (NC) type
iii) Change over (CO) type.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.6
Basics of Hydraulic System
2.5.2 Limit switches
− Any switch that is actuated due to the position of a fluid power component (usually a piston
rod or hydraulic motor shaft or the position of load is termed as limit switch. The actuation
of a limit switch provides an electrical signal that causes an appropriate system response.
− Limit switches perform the same function as push button switches. Push buttons are
manually actuated whereas limit switches are mechanically actuated.
− There are two types classification of Limit switches depending upon method of actuations
of contacts
a) Lever actuated contacts
b) Spring loaded contacts
− In lever type limit switches, the contacts are operated slowly. In spring type limit switches,
the contacts are operated rapidly. Figure 1.2 shows a simplified cross sectional view of a
limit switch and its symbol.
m
o
.c
e
T
c
e
ie
h
Figure 2.2 - Cross sectional view of a limit switch
2.5.3 Pressure switches
c
− A pressure switch is a pneumatic-electric signal converter. Pressure switches are used to
A
sense a change in pressure, and opens or closes an electrical switch when a predetermined
pressure is reached. Bellow or diaphragm is used to sense the change of pressure.
− Figure 1.3 shows a diaphragm type of pressure switch. When the pressure is applied at the
inlet and when the pre-set pressure is reached, the diaphragm expands and pushes the spring
loaded plunger to make/break contact.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.7
Basics of Hydraulic System
Figure 2.3 - Cross sectional view of a pressure switch
2.5.4 Solenoids
− Electrically actuated directional control valves form the interface between the two parts of
an electro-pneumatic control. The most important tasks of electrically actuated DCVs
include.
m
o
i) Switching supply air on or off
.c
ii) Extension and retraction of cylinder drives
− Electrically actuated directional control valves are switched with the aid of solenoids. They
can be divided into two groups:
ie
h
i)
Spring return valves only remain in the actuated position as long as current
flows through the solenoid
ii)
In the initial position, all solenoids of an electrically actuated DCVs are deenergized and the solenoids are inactive. A double valve has no clear initial
position, as it does not have a return spring. The possible voltage levels for
solenoids are 12 V DC, 12V AC, 12 V 50/60 Hz, 24V 50/60 Hz, 110/120V
50/60 Hz, 220/230V 50/60 Hz.
Double solenoid valves retain the last switched position even when no current
flows through the solenoid.
iii)
2.5.5 Relays
e
T
c
e
c
A
− A relay is an electro magnetically actuated switch. It is a simple electrical device used for
signal processing. Relays are designed to withstand heavy power surges and harsh
environment conditions. When a voltage is applied to the solenoid coil, an electromagnet
field results. This causes the armature to be attracted to the coil core.
− The armature actuates the relay contacts, either closing or opening them, depending on the
design. A return spring returns the armature to its initial position when the current to the coil
is interrupted. Cross sectional view of a relay is shown in Figure 1.4.
− A large number of control contacts can be incorporated in relays in contrast to the case of a
push button station. Relays are usually designated as K1, K2, and K3 etc. Relays also
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.8
Basics of Hydraulic System
possess interlocking capability that is an important safety feature in control circuits.
Interlocking avoids simultaneous switching of certain coils.
2.5.6 Timer or Time delay relays
− Timers are required in control systems to effect time delay between work operations. This is
possible by delaying the operation of the associated control element through a timer. Most
of the timers we use is Electronic timers. There are two types of time relay
m
o
.c
ie
h
Figure 2.4 - Cross sectional view of a relay
i) Pull in delay ( on –delay timer)
c
e
ii) Drop –out delay (off delay timer)
− In the on-delay timer, shown in Figure cc, when push button PB is pressed (ON), capacitor
C is charged through potentiometer R1 as diode D is reverse –biased. The time taken to
charge the capacitor, depends on the resistance of the potentiometer (R1) and the
capacitance(C) of the capacitor. By adjusting the resistance of the potentiometer, the
required time delay can be set. When the capacitor is charged sufficiently, coil K is
energized, and its contacts are operated after the set time delay. When the push button is
released (OFF), the capacitor discharges quickly through a small resistance (R2) as the
diode by passes resistor R1, and the contacts of relay (K) return to their normal position
without any delay.
e
T
c
A
− In the off-delay timer, the contacts are operated without any delay when the push button is
pressed (ON). The contacts return to the normal position after the set delay when the push
button is released (OFF).
− The construction and symbols of the on-delay and off-relay timers are given in Figure1.6
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.9
Basics of Hydraulic System
2.5.7 Temperature Switch
− Temperature switches automatically senses a change in temperature and opens or closes an
electrical switch when a predetermined temperature is reached. This switch can be wired
either normally open or normally closed.
− Temperature switches can be used to protect a fluid power system from serious damage
when a component such as a pump or strainer or cooler begins to malfunction.
m
o
.c
T
c
e
ie
h
Figure 2.5 - Construction features of timer and its symbols
e
c
A
Reference Books:
1. Industrial Hydraulics by John Pippenger and Tyler Hicks, McGraw Hill.
2. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
3. Fluid Power with Applications by Anthony Esposito, Pearson.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 2.10
Hydraulic Fluids
EXPERIMENT – 3
AIM – To study about hydraulic fluids and its properties
3.1 HYDRAULIC OILS AND FLUID PROPERTIES
A hydraulic fluid power system may be defined as a means of power transmission in which a
relatively incompressible fluid is used as the power transmitting media. The primary purpose
of a hydraulic system is the transfer of energy from one location to another and the
conversion of this energy to useful work. Hydraulic power is usually generated by pumps and
the energy generated is converted to useful work by hydraulic cylinders or other actuators
(linear or rotary). The transmission of this energy is accomplished by movement of the
hydraulic fluid through metal tubes or elastomeric hoses, while the control of the power is
achieved by means of values. As no hydraulic system can perform the assigned task without
the hydraulic fluid, this fluid is of utmost importance in a hydraulic system.
The broad tasks of hydraulic oil can be classified broadly as follows:
3. To avoid corrosion
4. To remove impurities and abrasion
5. To dissipate heat
c
e
3.2 TYPES OF HYDRAULIC FLUIDS
o
.c
l. To transfer hydraulic energy
2. To lubricate all parts
m
ie
h
There are different types of hydraulic fluids that have the required properties. In general
while selecting suitable fluid, a few important factors are to be considered.


T
Its compatibility with seals, bearing and other components.
Its viscosity and environmental stability are also considered.
e
c
1. Petroleum-based fluids: Mineral oils are the petroleum-based oils that are the most
commonly used hydraulic fluids. Basically, they possess most of the desirable characteristics:
they are easily available and are economical.
A
- In addition, they offer the best lubrication ability, least corrosion problems and are
compatible with most seal materials. The only major disadvantage of these fluids is their
flammability.
- They pose fire hazards, mainly from the leakages, in high-temperature environments such as
steel industries, etc. Mineral oils are good for operating temperatures below 50°C, at higher
temperatures, these oils lose their chemical stability and form acids, varnishes, etc.
- A petroleum oil is still by far the most highly used base for hydraulic fluids. In general,
petroleum oil has the following properties:
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.1
Hydraulic Fluids








Excellent lubricity
Higher demulsibility
More oxidation resistance
Higher viscosity index
Protection against rust
Good sealing characteristics
Easy dissipation of heat
Easy cleaning by filtration
A principal disadvantage of petroleum oil is that it burns easily. For applications where fire
could be a hazard, such as heat treating, hydroelectric welding, die casting, forging and many
others, there are several types of fire-resistant fluids available.
2. Emulsions: Emulsions are a mixture of two fluids that do not chemically react with others.
Emulsions of petroleum-based oil and water are commonly used. An emulsifier is normally
added to the emulsion, which keeps liquid as small droplets and remains suspended in the
other liquid. Two types of emulsions are in use:
m
o
A. Oil-in-water emulsions: This emulsion has water as the main phase, while small
droplets of oil are dispersed in it. Generally, the oil dilution is limited, about 5%;
hence, it exhibits the characteristics of water.
- Its limitations are poor viscosity, leading to leakage problems, loss in volumetric
efficiency and poor lubrication properties. These problems can be overcome to a
greater extent by using certain additives. Such emulsions are used in highdisplacement, low-speed pumps (such as in mining applications).
B. Water-in-oil emulsions: Water-in-oil emulsions, also called inverse emulsions, are
basically oil based in which small droplets of water are dispersed throughout the oil
phase.
- They are most popular fire-resistant hydraulic fluids. They exhibit more of an oillike characteristic; hence, they have good viscosity and lubrication properties.
- The commonly used emulsion has a dilution of 60% oil and 40% water. These
emulsions are good for operations at 25°C, as at a higher temperature, water
evaporates and leads to the loss of fire-resistant properties.
.c
e
T
c
e
ie
h
c
A
3. Water glycol: Water glycol is another non-flammable fluid commonly used in aircraft
hydraulic systems.
- It generally has a low lubrication ability as compared to mineral oils and is not suitable for
high-temperature applications. It has water and glycol in the ratio of 1:1. Because of its
aqueous nature and presence of air, it is prone to oxidation and related problems. It needs to
be added with oxidation inhibitors.
- Enough care is essential in using this fluid as it is toxic and corrosive toward certain metals
such as zinc, magnesium and aluminum. Again, it is not suitable for high-temperature
operations as the water may evaporate.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.2
Hydraulic Fluids
- However, it is very good for low-temperature applications as it possesses high antifreeze
characteristics.
4. Synthetic fluids: Synthetic fluid, based on phosphate ester, is another popular fireresistant fluid. It is suitable for high-temperature applications, since it exhibits good viscosity
and lubrication characteristics.
- It is not suitable for low-temperature applications.
- It is not compatible with common sealing materials such as nitrile. Basically being
expensive, it requires expensive sealing materials (viton).
- In addition, phosphate ester is not an environmental-friendly fluid. It also attacks aluminum
and paints.
5. Vegetable oils: The increase in the global pollution has led to the use of more
environmental-friendly fluids.
- Vegetable-based oils are biodegradable and are environmental safe. They have good
lubrication properties, moderate viscosity and are less expensive. They can be formulated to
have good fire resistance characteristics with certain additives.
- Vegetable oils have a tendency to easily oxidize and absorb moisture.
m
o
.c
- The acidity, sludge formation and corrosion problems are more severe in vegetable oils than
in mineral oils. Hence, vegetable oils need good inhibitors to minimize oxidation problems.
ie
h
6. Biodegradable: As more and more organizations are understanding their social
responsibility and are turning toward eco-friendly machinery and work regime, a
biodegradable hydraulic fluid is too becoming a sought after product in the dawn of an
environmentalist era.
c
e
- Biodegradable hydraulic fluids, alternatively known as bio-based hydraulic fluids, Biobased hydraulic fluids use sunflower, rapeseed, soybean, etc., as the base oil and hence cause
less pollution in the case of oil leaks or hydraulic hose failures.
T
- These fluids carry similar properties as that of a mineral oil–based anti-wear hydraulic fluid,
Hypothetically, if a company plans to introduce bio-based fluids into the hydraulic
components of the machinery and the permissible operating pressure of hydraulic
components is reduced to 80%, then it would inversely lead to a 20% reduction in breakingout force owing to the 20% reduction in excavator’s operating pressure.
e
c
A
- It is so because a reduction in the operating pressure of a system leads to a reduction in
actuator force.
- Besides, the transformation would not only include the cost of fluid and flushing of
machinery to transcend from a mineral oil to vegetable oil repeatedly but also include the
derating costs of machinery.
7. Fire Resistance: There are many hazardous applications where human safety requires the
use of a fire-resistant fluid. Examples include coal mines, hot metal processing equipment,
aircraft and marine fluid power systems.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.3
Hydraulic Fluids
- A fire-resisting fluid is one that can be ignited but does not support combustion when the
ignition source is removed.
- Flammability is defined as the ease of ignition and ability to propagate the flame.
- The following are the usual characteristics tested in order to determine the flammability of
hydraulic fluids:
- The fire-resistant fluids are designated as follows:
1. HFA: A high-water-content fluid or HWCF (80% or more), for example, water–oil
emulsions.
2. HFB: This is water–oil emulsion containing petroleum oil and water.
3. HFC: This is a solution of water and glycol.
4. HFD: This is a synthetic fluid, for example, phosphates or phosphate–petroleum
blends.
- The commonly used hydraulic liquids are petroleum derivatives; consequently, they burn
vigorously once they reach a fire point. For critical applications, artificial or synthetic
hydraulic fluids are used that have fire resistance.
m
o
.c
1. Water–glycol solution: This type consists of an actual solution of 40% water and
60% glycol. These solutions have high-viscosity-index values, but as the viscosity rises, the
water evaporates. The operating temperature ranges run from −20°C to about 85°C.
ie
h
2. Water-in-oil emulsions: This type consists of about 40% water completely
dispersed in a special oil base. It is characterized by small droplets of water completely
surrounded by oil. The operating temperature range runs from −30°C to about 80°C. As is the
case with water–glycol solutions, it is necessary to replenish evaporated water to maintain
proper viscosity.
c
e
3. Straight synthetics: This type is chemically formulated to inhibit combustion and
in general has the highest fire-resistant temperature. The disadvantages of straight synthetics
include low viscosity index, incompatibility with most natural or synthetic rubber seals and
high cost.
e
T
c
4. High-water-content fluids (HWCFs): This type consists of about 90% water and
10% concentrate (designated as 90/10). The concentrate consists of fluid additives that
improve viscosity, lubrication, rust protection and protection against bacteria growth. The
maximum operating temperature should be held to 50°C to minimize evaporation.
A
- The advantages of HWCF are as follows:
1. Fire resistance due to a high flash point of about 150°C.
2. Lower system operating temperature due to good heat dissipation.
3. Biodegradable and environmental-friendly additives.
4. High viscosity index.
5. Cleaner operation of the system.
6. Low cost of concentrate and storage.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.4
Hydraulic Fluids
- The disadvantages of HWCF are as follows:
1. Greater contamination due to higher densities of fluids.
2. High evaporation loss.
3. Faster corrosion due to oxidation.
4. pH value to be maintained between 7.5 and 9.0.
5. Promotion of bacterial growth and filtration difficulties due to the acidic nature of
fluids.
Performance of HWCFs can be improved using additives such as
1. Anti-wear additives.
2. Anti-foaming additives.
3. Corrosion inhibitors.
4. Biocides to kill water-borne bacteria.
5. Emulsifying agents.
6. Flocculation promoters.
7. Deionization agents.
8. Oxidation inhibitors.
m
9. Anti-vaporizing agents.
o
3.3 PROPERTIES OF FLUIDS
.c
For a fluid to perform efficiently, it must possess certain properties. The various properties
required for an ideal hydraulic fluid are as follows:
1. Ideal viscosity.
2. Good lubrication capability.
3. Demulsibility.
c
e
ie
h
4. Good chemical and environmental stability.
5. Incompressibility.
6. Fire resistance.
T
7. Low flammability.
e
8. Foam resistance.
c
9. Low volatility.
A
10. Good heat dissipation.
11. Low density.
12. System compatibility.
- It is almost impossible to achieve all these properties in a hydraulic fluid. Although we can
select a good fluid with desirable properties, some of the characteristics of a fluid change
with usage.
- For example, it is common for the temperature of a fluid to rise due to friction in the system,
which reduces the viscosity of the fluid, which in turn increases leakage and reduces
lubrication ability.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.5
Hydraulic Fluids
- A fluid gets oxidized and becomes acidic with usage. Certain additives are added to
preserve the desirable properties and to make the fluid more stable.
- Some of the desirable properties and their influence on a hydraulic fluid are discussed
briefly in the following sub-sections.
Ideal Viscosity
- The most basic desirable property of a hydraulic fluid is optimum viscosity. It is a measure
of a fluid’s resistance to flow.
1. High viscosity:
 High resistance to flow.
 Increased power consumption due to frictional loss.
 High temperature caused by friction.
 Increased pressure drop because of the resistance.


Possibility of sluggish or slow operation.
Difficulty in separating air from oil in a reservoir.
m
 Greater vacuum at the pump inlet, causing cavitation. Higher system noise level.
2. Low viscosity:
 Increased internal leakage.
 Excessive water.
o
.c
 Possibility of decreased pump efficiency, causing slower operation of the
ie
h
actuator. Increased temperature resulting from leakage losses.
Lubrication Capability
- Hydraulic oil should have a good lubricating property. That is, the film so formed should be
strong enough that it is not wiped out by the moving parts.
Demulsibility
T
c
e
- The ability of a hydraulic fluid to separate rapidly from moisture and successfully resist
emulsification is known as “demulsibility.”
e
- If an oil emulsifies with water, the emulsion promotes the destruction of lubricating and
sealant properties. Highly refined oils are basically water resistant by nature.
c
A
Good Chemical and Environmental Stability (Oxidation and Corrosion Resistance)
- For a good hydraulic fluid, a good chemical and environmental stability is desirable. Most
fluids are vulnerable to oxidation, as they come in contact with oxygen in air.
- Mineral oils or petroleum-based oils (widely used in hydraulic systems) contain carbon and
hydrogen molecules, which easily react with oxygen.
- The oxidation products are highly soluble in oil and being acidic in nature they can easily
corrode metallic parts.
- The soluble acidic products cause corrosion, whereas insoluble products make the operation
sluggish. Oxidation leads to deterioration in the chemical nature of fluid, which may form
some chemical sledges, gum or varnish at low velocity or stagnation points in the system.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.6
Hydraulic Fluids
- Many factors influence the rate of oxidation, such as temperature, pressure, moisture and so
on. Temperature is the most affecting one, as the rate of oxidation increases severely with rise
in temperature.
- The moisture entering the hydraulic system with air causes the parts made of ferrous
materials to rust. Rust is a chemical reaction between iron or steel and oxygen.
- Corrosion, on the other hand, is the chemical reaction between a metal and an acid. The
result of rusting and corrosion is the “eating away” of the metal surfaces of the hydraulic
components. Rust and corrosion cause excessive leakage between moving parts.
Neutralization Numbers
- Neutralization number is a measure of the acidity or alkalinity of hydraulic oil. This is
referred to as the pH value of the oil. High acidity causes the oxidation rate in oil to increase
rapidly.
Low Flammability
m
- It refers to the ease with which a fluid gets ignited and propagates the flame. Hence, it is
desirable to have a low flammability for a hydraulic fluid.
o
Foam Resistance
.c
- Air can be present in a hydraulic fluid in two forms: dissolved and entrained. For example,
if the return line to the reservoir is not submerged, the jet of oil entering the liquid surface
will carry air with it.
ie
h
- This causes air bubbles to form in the oil. If these bubbles rise to the surface too slowly,
they will be drawn into the pump intake. This can cause pump damage due to cavitation.
Low Volatility
c
e
- A fluid should possess low vapour pressure or high boiling point. The vapour pressure of a
fluid varies with temperature and hence the operating temperature range of the system is
important in determining the stability of the fluid.
e
Good Heat Dissipation
T
c
- A hydraulic fluid should have a high heat dissipation capability. The temperature of a fluid
shoots up if its heat dissipation characteristics are poor.
A
Low Density
- The relative density of a mineral oil is 0.9 (the exact value depends on the base oil and the
additive used). Synthetic fluids can have a relative density greater than 1.
System Compatibility
- A hydraulic fluid should be inert to materials used in or near the hydraulic equipment. If the
fluid in anyway attacks, destroys, dissolves or changes the parts of hydraulic system, the
system may lose its functional efficiency and may start malfunction.
Stable Chemically and Physically
- Fluid characteristics should remain unchanged during an extended useful life and during
storage.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.7
Hydraulic Fluids
- The fluid in a working hydraulic system is subjected to violent usage-large pressure
fluctuations, shock, turbulence, aeration, cavitation, water and particulate contamination, high
shear rates, and large temperature variations.
- Since many aspects of stability are chemical in nature, the temperatures to which the fluid
will be exposed is an important criterion in the selection of a. hydraulic fluid.
Good Heat Dissipation
- An important requirement of the fluid is to carry heat away from the working parts. Pressure
drops, mechanical friction, fluid friction, leakages, all generate heat.
- The fluid must carry the generated heat away and readily dissipate it to the atmosphere or
coolers. Therefore high thermal conductivity and high specific heat values are desirable in the
fluid chosen.
High Bulk Modulus
- In general, oil is taken as incompressible. However, in practice, all materials are
compressible and so is oil.
m
- The bulk modulus is a measure of the degree of compressibility of the fluid and is the
reciprocal of compressibility.
o
.c
- The higher the bulk modulus, the lesser the material will be compressed with increasing
pressure.
ie
h
- Bulk modulus is an important characteristic of a hydraulic fluid because of control
problems, especially in servo hydraulics.
Low Coefficient of Expansion
c
e
- A low coefficient of expansion is usually desirable in a hydraulic fluid to minimise the total
volume of the system required at the operating temperature.
3.4 PHYSICAL CHARACTERISTICS OF HYDRAULIC FLUID
Density
e
T
- Density may be defined as the mass of oil per unit volume. The unit will be kg/cm 3 or
kg/m3.
c
A
𝑚𝑎𝑠𝑠
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 (𝜌) = 𝑣𝑜𝑙𝑢𝑚𝑒
- Density of any liquid is generally measured by an instrument called hydrometer. If one dips
the instrument into the liquid or oil, the density can be directly read.
- Hydraulic oils which are used in industrial hydraulic systems may have a density of 0.8 to
0.9 gm/cm3.
Table 3.1 - Density characteristics of hydraulic fluids
Fluid
Density (kg/m3)
Shell Tellus ISO 32 mineral oil
875
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.8
Hydraulic Fluids
Shell HFB 60%oil,40%oil
933
Shell HFC 60%glycol,40%water
1084
1125
Shell HFD phosphate ester
918
Shell Naturelle HFE 32
Specific Gravity
- Specific gravity of oil is defined as the ratio of densities of oil and water. Specific gravity of
a fluid is important in those cases where the overall system weight must be kept minimum.
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 =
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑜𝑖𝑙
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟
- As per standards, density of water is accepted as 1. Hence if we say that the specific gravity
of oil is 0.80, then the logical inference is that the oil in question has a density of 0.8 gm/cm3.
m
- Specific gravity and density may seem to be the same; it is necessary that we understand the
mathematical relationship so that while solving problems we are not confused.
o
.c
- A heavy fluid can cause pump cavitation and resultant malfunction of the system.
Specific Weight
ie
h
- Specific weight of hydraulic oil is calculated by multiplying density of oil by acceleration
due to gravity.
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑊𝑒𝑖𝑔ℎ𝑡 (𝛾) =
Viscosity
c
e
𝑊𝑒𝑖𝑔ℎ𝑡
𝑉𝑜𝑙𝑢𝑚𝑒
- Viscosity is a very important property of oil. It is the measure of the ability of e liquid to
flow. It can actually be defined as the resistance to flow.
e
T
- To understand the physical concept of viscosity, let us take few simple examples. When or swims in a pool of water, one experiences a resistance to the motion.
c
- One might have noticed that when a liquid kept in a container is stirred and left to itself.6c
motion will disappear after sometime. This indicates that there is some kind d frictional force
in all types of fluids. This force is called the viscous force.
A
Reference Books:
1. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 3.9
Hydraulic Pumps and actuators
EXPERIMENT – 4
AIM – To study about hydraulic pumps and actuators
4.1 HYDRAULIC PUMPS
A pump will have an inlet called suction and an outlet called delivery. It converts mechanical
energy in to hydraulic energy. Pump is also known as heart of hydraulic system. The basic
principle is that due to mechanical action, the pump created partial vacuum at its inlet. This
permits atmospheric pressure to force the fluid through the inlet line and in to the pump, then
pump pushes the fluid into the hydraulic system.
− These are mainly classified into two categories:
(a) Non-positive displacement pumps (Hydrodynamic/ Rotodynamic)
(b) Positive displacement pumps (Hydrostatic)
m
o
.c
e
T
c
e
ie
h
c
A
4.1.1 Gear Pumps
− Gear pump is a robust and simple positive displacement pump. It has two meshed gears
revolving about their respective axes. These gears are the only moving parts in the pump.
They are compact, relatively inexpensive and have few moving parts. The rigid design of the
gears and houses allow for very high pressures and the ability to pump highly viscous fluids.
These pump includes helical and herringbone gear sets (instead of spur gears), lobe shaped
rotors similar to Roots blowers (commonly used as superchargers), and mechanical designs
that allow the stacking of pumps. Based upon the design, the gear pumps are classified as:
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.1
Hydraulic Pumps and actuators
(a) External gear pumps
(b) Lobe pumps
(c) Internal gear pumps
− Generally gear pumps are used to pump:
• Petrochemicals: Pure or filled bitumen, pitch, diesel oil, crude oil, lube oil etc.
• Chemicals: Sodium silicate, acids, plastics, mixed chemicals, isocyanates etc.
• Paint and ink
• Resins and adhesives
• Pulp and paper: acid, soap, lye, black liquor, kaolin, lime, latex, sludge etc.
• Food: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, molasses,
animal food etc.
(a) External gear pumps
m
− The external gear pump consists of externally meshed two gears housed in a pump case as
shown in figure 4.1 one of the gears is coupled with a prime mover and is called as driving
gear and another is called as driven gear.
o
.c
− The rotating gear carries the fluid from the tank to the outlet pipe. The suction side is
towards the portion whereas the gear teeth come out of the mesh.
ie
h
− When the gears rotate, volume of the chamber expands leading to pressure drop below
atmospheric value. Therefore the vacuum is created and the fluid is pushed into the void due
to atmospheric pressure. The fluid is trapped between housing and rotating teeth of the gears.
c
e
− The discharge side of pump is towards the portion where the gear teeth run into the mesh
and the volume decreases between meshing teeth.
T
− The clearance between gear teeth and housing and between side plate and gear face is very
important and plays an important role in preventing leakage. In general, the gap distance is
less than 10 micro meters. The amount of fluid discharge is determined by the number of gear
teeth, the volume of fluid between each pair of teeth and the speed of rotation.
e
c
− Gear pumps are most commonly used for the hydraulic fluid power applications and are
widely used in chemical installations to pump fluid with a certain viscosity.
A
Figure 4.1 - External gear pump
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.2
Hydraulic Pumps and actuators
(b) Lobe pumps
− Lobe pumps work on the similar principle of working as that of external gear pumps.
However in Lobe pumps, the lobes do not make any contact like external gear pump (see
Figure 4.2).
− Now, the fluid flows into the cavity and is trapped by the lobes. Fluid travels around the
interior of casing in the pockets between the lobes and the casing. Finally, the meshing of the
lobes forces liquid to pass through the outlet port. The bearings are placed out of the pumped
liquid. Therefore the pressure is limited by the bearing location and shaft deflection.
− Lobe pumps are widely used in industries such as pulp and paper, chemical, food,
beverage, pharmaceutical and biotechnology etc.
− These pumps can handle solids (e.g., cherries and olives), slurries, pastes, and a variety of
liquids. A gentle pumping action minimizes product degradation.
m
o
.c
ie
h
Figure 4.2 - Lobe pump
(c) Internal gear pumps
c
e
− Internal gear pumps are exceptionally versatile. They are often used for low or medium
viscosity fluids such as solvents and fuel oil and wide range of temperature. This is nonpulsing, self-priming and can run dry for short periods. It is a variation of the basic gear
pump.
e
T
c
− It comprises of an internal gear, a regular spur gear, a crescent-shaped seal and an external
housing. The schematic of internal gear pump is shown in Figure 4.3.
A
− Liquid enters the suction port between the rotor (large exterior gear) and idler (small
interior gear) teeth. Liquid travels through the pump between the teeth and crescent. Crescent
divides the liquid and acts as a seal between the suction and discharge ports.
− When the teeth mesh on the side opposite to the crescent seal, the fluid is forced out
through the discharge port of the pump. This clearance between gears can be adjusted to
accommodate high temperature, to handle high viscosity fluids and to accommodate the wear.
− However, these pumps are not suitable for high speed and high pressure applications. Only
one bearing is used in the pump therefore overhung load on shaft bearing reduces the life of
the bearing.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.3
Hydraulic Pumps and actuators
m
Figure 4.3 - Internal gear pump
4.1.2 Vane Pumps
o
.c
− In the previous topic we have studied the gear pumps. These pumps have a disadvantage of
small leakage due to gap between gear teeth and the pump housing. This limitation is
overcome in vane pumps.
ie
h
− The leakage is reduced by using spring or hydraulically loaded vanes placed in the slots of
driven rotor.
− Vane pumps are available in a number of vane configurations including sliding vane,
flexible vane, swinging vane, rolling vane, and external vane etc.
c
e
− The operating range of these pumps varies from -32 °C to 260 °C.
T
− The schematic of vane pump working principle is shown in figure 4.4 Vane pumps generate
a pumping action by tracking of vanes along the casing wall.
e
− The vane pumps generally consist of a rotor, vanes, ring and a port plate with inlet and
outlet ports.
c
A
Figure 4.4 - Schematic of working principle of vane pump
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.4
Hydraulic Pumps and actuators
− The rotor in a vane pump is connected to the prime mover through a shaft. The vanes are
located on the slotted rotor.
− The rotor is eccentrically placed inside a cam ring as shown in the figure. The rotor is
sealed into the cam by two side plates.
− When the prime mover rotates the rotor, the vanes are thrown outward due to centrifugal
force. The vanes track along the ring.
− It provides a tight hydraulic seal to the fluid which is more at the higher rotation speed due
to higher centrifugal force. This produces a suction cavity in the ring as the rotor rotates. It
creates vacuum at the inlet and therefore, the fluid is pushed into the pump through the inlet.
The fluid is carried around to the outlet by the vanes whose retraction causes the fluid to be
expelled.
− The capacity of the pump depends upon the eccentricity, expansion of vanes, and width of
vanes and speed of the rotor. It can be noted that the fluid flow will not occur when the
eccentricity is zero.
m
− These pumps can handle thin liquids (low viscosity) at relatively higher pressure.
o
− However, these pumps are not suitable for high speed applications and for the high
viscosity fluids or fluids carrying some abrasive particles.
.c
− The maintenance cost is also higher due to many moving parts. These pumps have various
applications for the pumping of following fluids:
• Aerosol and Propellants
ie
h
• Aviation Service - Fuel Transfer, Deicing
c
e
• Auto Industry - Fuels, Lubes, Refrigeration Coolants
• Bulk Transfer of LPG and NH3
• LPG Cylinder Filling
e
T
c
A
Figure 4.5 - Unbalanced vane pump
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.5
Hydraulic Pumps and actuators
− In practice, the vane pumps have more than one vane as shown in figure 4.5. The rotor is
offset within the housing, and the vanes are constrained by a cam ring as they cross inlet and
outlet ports.
− Although the vane tips are held against the housing, still a small amount of leakage exists
between rotor faces and body sides.
− Also, the vanes compensate to a large degree for wear at the vane tips or in the housing
itself. The pressure difference between outlet and inlet ports creates a large amount of load on
the vanes and a significant amount of side load on the rotor shaft which can lead to bearing
failure. This type of pump is called as unbalanced vane pump.
m
o
.c
ie
h
Figure 4.6 - Adjustable vane pump
4.1.3 Piston Pumps
c
e
− Piston pumps are meant for the high-pressure applications. These pumps have highefficiency and simple design and needs lower maintenance. These pumps convert the rotary
motion of the input shaft to the reciprocating motion of the piston. These pumps work similar
to the four stroke engines.
e
T
c
− They work on the principle that a reciprocating piston draws fluid inside the cylinder when
the piston retracts in a cylinder bore and discharge the fluid when it extends. These pumps are
positive displacement pump and can be used for both liquids and gases. Piston pumps are
basically of two types:
A
(a) Axial piston pumps
(b) Radial piston pumps
(a) Axial piston pumps
− Axial piston pumps are positive displacement pumps which converts rotary motion of the
input shaft into an axial reciprocating motion of the pistons. These pumps have a number of
pistons (usually an odd number) in a circular array within a housing which is commonly
referred to as a cylinder block, rotor or barrel. These pumps are used in jet aircraft.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.6
Hydraulic Pumps and actuators
− These pumps have sub-types as:
1. Bent axis piston pump
2. Swash plate axial piston pump
1. Bent axis piston pump
− Figure 4.7 shows the schematic of bent axis piston pump. In these pumps, the reciprocating
action of the pistons is obtained by bending the axis of the cylinder block.
− The cylinder block rotates at an angle which is inclined to the drive shaft. The cylinder
block is turned by the drive shaft through a universal link.
− The cylinder block is set at an offset angle with the drive shaft. The cylinder block contains
a number of pistons along its periphery. These piston rods are connected with the drive shaft
flange by ball-and-socket joints.
− The volumetric displacement (discharge) of the pump is controlled by changing the offset
angle. It makes the system simple and inexpensive.
m
2. Swash plate axial piston pump
o
− A swash plate is a device that translates the rotary motion of a shaft into the reciprocating
motion. It consists of a disk attached to a shaft as shown in Figure 4.8. If the disk is aligned
perpendicular to the shaft; the disk will turn along with the rotating shaft without any
reciprocating effect.
.c
ie
h
− In swash plate axial piston pump a series of pistons are aligned coaxially with a shaft
through a swash plate to pump a fluid. The schematic of swash plate piston pump is shown in
Figure 4.8. The axial reciprocating motion of pistons is obtained by a swash plate that is
either fixed or has variable degree of angle.
e
T
c
e
c
A
Figure 4.7 - Bent axis piston pump
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.7
Hydraulic Pumps and actuators
Figure 4.8 - Swash plate axial piston pump
(b) Radial piston pumps
m
o
− The typical construction of radial piston pump is shown in Figure 4.9. The piston pump has
pistons aligned radially in a cylindrical block. It consists of a pintle, a cylinder barrel with
pistons and a rotor containing a reaction ring. The pintle directs the fluid in and out of the
cylinder. Pistons are placed in radial bores around the rotor.
.c
ie
h
− The piston shoes ride on an eccentric ring which causes them to reciprocate as they rotate.
The eccentricity determines the stroke of the pumping piston. Each piston is connected to
inlet port when it starts extending while it is connected to the outlet port when start retracting.
This connection to the inlet and outlet port is performed by the timed porting arrangement in
the pintle.
c
e
− As the cylinder barrel rotates, the pistons on one side travel outward. This draws the fluid
in as the cylinder passes the suction port of the pintle. It is continued till the maximum
eccentricity is reached. When the piston passes the maximum eccentricity, pintle is forced
inwards by the reaction ring. This forces the fluid to flow out of the cylinder and enter in the
discharge (outlet) port of the pintle.
e
T
c
A
Figure 4.9 - Radial piston pump
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.8
Hydraulic Pumps and actuators
4.2 LINEAR ACTUATORS
Reliability of hydraulic system not only depends on the system design but also on factors
such as component design and manufacturing and their correct choice. This is also correct
while selecting the cylinder.
A correct cylinder in a hydraulic system contributes to:
1.
2.
3.
4.
5.
Optimize system maintainability
Ensure minimum down time
Ease the process of repairing and trouble shooting
Ensure maximum work accuracy
Maintain least economic liability and financial losses
4.3 TYPES OF CYLINDER
Functionally cylinders are classified as:
1.
2.
3.
4.
Single acting cylinders
Double acting cylinder
Telescopic cylinders
Tandem cylinders
m
o
.c
1. Single-Acting Cylinders
− A single-acting cylinder is simplest in design and is shown schematically in Fig 4.10. It
consists of a piston inside a cylindrical housing called barrel. On one end of the piston there
is a rod, which can reciprocate. At the opposite end, there is a port for the entrance and exit of
oil.
ie
h
− Single-acting cylinders produce force in one direction by hydraulic pressure acting on the
piston. (Single-acting cylinders can exert a force in the extending direction only.) The return
of the piston is not done hydraulically. In single-acting cylinders, retraction is done either by
gravity or by a spring.
e
T
c
e
c
A
Figure 4.10 - Single-acting cylinders
According to the type of return, single-acting cylinders are classified as follows:
 Gravity-return single-acting cylinder
 Spring-return single-acting cylinder
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.9
Hydraulic Pumps and actuators
Spring-Return Single-Acting Cylinder
− A spring-return single-acting cylinder is shown in Fig.4.11.In push type [Fig. 4.11 (a)], the
pressure is sent through the pressure port situated at the blank end of the cylinder.
− When the pressure is released, the spring automatically returns the cylinder to the fully
retracted position. The vent port is open to atmosphere so that air can flow freely in and out
of the rod end of the cylinder.
− Figure 4.11 (b) shows a spring-return single-acting cylinder. In this design, the cylinder
retracts when the pressure port is connected to the pump flow and extends whenever the
pressure port is connected to the tank. Here the pressure port is situated at the rod end of the
cylinder.
m
o
.c
Figure 4.11 - (a) Push- and (b) pull-type single-acting cylinders
2. Double-Acting Cylinder
There are two types of double-acting cylinders:


ie
h
Double-acting cylinder with a piston rod on one side.
Double-acting cylinder with a piston rod on both sides.
3. Telescopic Cylinder
c
e
− A telescopic cylinder (shown in Fig. 4.12) is used when a long stroke length and a short
retracted length are required. The telescopic cylinder extends in stages, each stage consisting
of a sleeve that fits inside the previous stage.
e
T
− One application for this type of cylinder is raising a dump truck bed. Telescopic cylinders
are available in both single-acting and double-acting models. They are more expensive than
standard cylinders due to their more complex construction.
c
A
− They generally consist of a nest of tubes and operate on the displacement principle. The
tubes are supported by bearing rings, the innermost (rear) set of which have grooves or
channels to allow fluid flow.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.10
Hydraulic Pumps and actuators
Figure 4.12 - Telescopic cylinder
− For a given input flow rate, the speed of operation increases in steps as each successive
section reaches the end of its stroke. Similarly, for a specific pressure, the load-lifting
capacity decreases for each successive section.
m
o
4. Tandem Cylinder
.c
ie
h
Figure 4.13 - Tandem cylinder
c
e
− A tandem cylinder, shown in Fig. 4.13, is used in applications where a large amount of
force is required from a small-diameter cylinder. Pressure is applied to both pistons, resulting
in increased force because of the larger area.
T
− The drawback is that these cylinders must be longer than a standard cylinder to achieve an
equal speed because flow must go to both pistons.
e
c
5. Diaphragrn Cylinder
A
− These are used for very small displacements. There will be a diaphragm instead of piston
inside the cylinder. The diaphragm deflects when working fluid is admitted into the cylinder.
− The diaphragm is fitted with a piston rod and hence the piston rod extends or retracts.
− Applications: Food industries, Milk dairies, Air brake etc.
4.4 ROTARY ACTUATORS
− Hydraulic motors are rotary actuators. However, the name rotary actuator is reserved for a
particular type of unit that is limited in rotation to less than 360 degree.
− A hydraulic motor is a device which converts fluid power into rotary power or converts
fluid pressure into torque.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.11
Hydraulic Pumps and actuators
− Torque is a function of pressure or, in other words, the motor input pressure level is
determined by the resisting torque at the output shaft. A hydraulic pump is a device which
converts mechanical force and motion into fluid power.
− A hydraulic motor is not a hydraulic pump when run backward. A design that is completely
acceptable as a motor may operate very poorly as a pump in a certain applications.
4.3.1 Applications
− Hydraulic motors have become popular in industries. Hydraulic motors can be applied
directly to the work. They provide excellent control for acceleration, operating speed,
deceleration, smooth reversals and positioning.
− They also provide flexibility in design and eliminate much of bulk and weight of
mechanical and electrical power transmission.
− The applications of hydraulic motors in their various combinations with pumping units are
termed hydrostatic transmission.
m
− A hydrostatic transmission converts mechanical power into fluid power and then reconverts
o
fluid power into shaft power. The advantages of hydrostatic transmissions include power
transmission to remote areas, infinitely variable speed control, self-overload protection,
reverse rotation capability, dynamic braking and a high power-to-weight ratio. Applications
include material-handling equipment, farm tractors, railway locomotives, buses, lawn
mowers and machine tools.
.c
ie
h
− New fields of applications are being discovered constantly for hydrostatic transmissions.
Farm implements, road machinery, material-handling equipment, Numerical Control(NC)
machines high-performance aircrafts, military uses and special machinery are only a few of
new fields expanding through the use of fluid power transmission. Many automobiles,
railway locomotives and buses use a hydrostatic transmission.
c
e
4.5 CLASSIFICATION OF HYDRAULIC MOTORS
T
− There are two types of hydraulic motors: (a) High-speed low-torque motors and (b) low–
e
speed high-torque motors. In high-speed low-torque motors, the shaft is driven directly from
either the barrel or the cam plate, whereas in low-speed high-torque motors, the shaft is
driven through a differential gear arrangement that reduces the speed and increases the
torque.
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.12
Hydraulic Pumps and actuators
− Depending upon the mechanism employed to provide shaft rotation, hydraulic motors can
be classified as follows:
1. Gear motors.
2. Vane motors.
3. Piston motors:

Axial piston-type motors.

Radial piston-type motors.
m
Reference Books:
1. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
2. Fluid Power with Applications by Anthony Esposito, Pearson.
o
.c
e
T
c
e
ie
h
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 4.13
Control Valves
EXPERIMENT – 5
AIM – To study about different types of control valves used in hydraulic system
5.1 CONTROL VALVES
 In a hydraulic system, the hydraulic energy available from a pump is converted into
motion and force by means of an actuator. The control of these mechanical outputs
(motion and force) is one of the most important functions in a hydraulic system. The
proper selection of control selection ensures the desired output and safe function of the
system. In order to control the hydraulic outputs, different types of control valves are
required. It is important to know various types of control valves and their functions. This
not only helps to design a proper hydraulic system but also helps to discover the
innovative ways to improve the existing systems.
o
 There are basically three types of valves employed in hydraulic systems:
.c
1. Directional control valves
2. Flow control valves
3. Pressure control valves
5.2 DIRECTION CONTROL VALVE
m
ie
h
− Directional control valves are used to control the distribution of energy in a fluid power
system. They provide the direction to the fluid and allow the flow in a particular direction.
c
e
− These valves are used to control the start, stop and change in direction of the fluid flow.
These valves regulate the flow direction in the hydraulic circuit.
T
− Directional control valves can be classified in the following manner:
e
1. Type of construction:
c
• Poppet valves
A
• Spool valves
2. Number of ports:
• Two- way valves
• Three – way valves
• Four- way valves.
3. Number of switching position:
• Two – position
• Three - position
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.1
Control Valves
4. Actuating mechanism:
• Manual actuation
• Mechanical actuation
• Solenoid actuation
• Hydraulic actuation
• Pneumatic actuation
• Indirect actuation
1. Type of construction
Check Valves
m
o
.c
c
e
ie
h
Figure 5.1 - Check valve
− These are unidirectional valves and permit the free flow in one direction only. These valves
have two ports: one for the entry of fluid and the other for the discharge.
e
T
− They are consists of a housing bore in which ball or poppet is held by a small spring force.
The valve having ball as a closing member is known as ball check valve.
c
− The various types of check valves are available for a range of applications. These valves
are generally small sized, simple in construction and inexpensive.
A
− Generally, the check valves are automatically operated. Human intervention or any external
control system is not required.
− These valves can wear out or can generate the cracks after prolonged usage and therefore
they are mostly made of plastics for easy repair and replacements. The check valve is
designed for a specific cracking pressure which is the minimum upstream pressure at which
the valve operates.
− The ball is held against the valve seat by a spring force. It can be observed from the figure
that the fluid flow is not possible from the spring side but the fluid from opposite side can
pass by lifting the ball against.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.2
Control Valves
− However, there is some pressure drop across the valve due to restriction by the spring force.
Therefore these valves are not suitable for the application of high flow rate. When the
operating pressure increases the valve becomes more tightly seated in this design.
− Some valves are meant for an application where free flow is required in one direction and
restricted flow required in another direction. These types of valves are called as restriction
check valve. These valves are used when a direction sensitive flow rate is required. For
example, the different actuator speeds are required in both the directions. The flow
adjustment screw can be used to set the discharge (flow rate) in the restricted direction.
m
o
.c
ie
h
Figure 5.2 - Restriction check valve
Spool valve
c
e
− The spool valves derive their name from their appearance. It consists of a shaft sliding in a
bore which has large groove around the circumference.
T
− This type of construction makes it look like a spool. The spool is sealed along the clearance
between moving spool and housing (valve body).
e
− The quality of seal or the amount of leakage depends on the amount of clearance, viscosity
of fluid and the level of the pressure.
c
A
− The grooves guide the fluid flow by interconnecting or blocking the holes (ports). The
spool valves are categorized according to the number of operating positions and the way
hydraulic lines interconnections.
− One of the simplest two way spool valve is shown in Figure 4.4. The standard terms are
referred as Port ‘P’ is pressure port, Port ‘T’ is tank port and Port ‘A’ and Port ‘B’ are the
actuator (or working) ports. The actuators can move in forward or backward direction
depending on the connectivity of the pressure and tank port with the actuators port.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.3
Control Valves
Figure 5.3 - Valve closed
Figure 5.4 - Valve opened by actuation
2. Number of ports
m
o
.c
Three way valves
e
T
c
e
ie
h
Figure 5.5- Three way valve: P to A connected and T is blocked
c
A
Figure 5.6 - Three way valve in closed position
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.4
Control Valves
Four way valves with types of center conditions
Figure 5.7 - Three position four way valve in open center mode
m
o
.c
Figure 5.8 - Three position four way valve: P to B and A to T.
T
c
e
ie
h
Figure 5.9 - Three position four way valve: P to A and B to T
e
c
A
Figure 5.10 - Three position four way valve: closed center
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.5
Control Valves
Figure 5.11 - Tandem centered valve
m
o
.c
Figure 5.12 - Regenerative Center
e
T
c
e
ie
h
Figure 5.13 - Floating Center
4. Classification based on actuation mechanism
c
Manual actuation
A
In this type, the spool is operated manually. Manual actuators are hand lever, push button and
pedals etc.
Mechanical actuation
− The DCV spool can be operated by using mechanical elements such as roller and cam,
roller and plunger and rack and pinion etc. In these arrangements, the spool end is of roller or
a pinion gear type. The plunger or cam or rack gear is attached to the actuator. Thus, the
mechanical elements gain some motion relative to the actuator (cylinder piston) which can be
used for the actuation.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.6
Control Valves
Solenoid actuation
− The solenoid actuation is also known as electrical actuation. The schematic of solenoid
actuation is shown in Figure 5.14. The energized solenoid coil creates a magnetic force which
pulls the armature into the coil. This movement of armature controls the spool position. The
main advantage of solenoid actuation is its less switching time.
Figure 5.14 - Working of solenoid to shift spool of valve
Hydraulic actuation
m
− This type actuation is usually known as pilot-actuated valve and a schematic is shown in
Figure 5.15. In this type of actuation, the hydraulic pressure is directly applied on the spool.
The pilot port is located on one end of the valve. Fluid entering from pilot port operates
against the piston and forces the spool to move forward. The needle valve is used to control
the speed of the actuation.
o
.c
e
T
c
e
ie
h
Figure 5.15 - Pilot actuated DCV
c
Pneumatic actuation
A
− DCV can also be operated by applying compressed air against a piston at either end of the
valve spool. The construction of the system is similar to the hydraulic actuation as shown in
Figure 5.15. The only difference would be the actuation medium. The actuation medium is
the compressed air in pneumatic actuation system.
Indirect actuation of directional control valve
− The direction control valve can be operated by manual, mechanical, solenoidal (electrical),
hydraulic (pilot) and pneumatic actuations. The mode of actuation does not have any
influence on the basic operation of the hydraulic circuits.
− Mostly, the direct actuation is restricted to use with smaller valves only because usually lot
of force is not available. The availability of limited force is the greatest disadvantage of the
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.7
Control Valves
direct actuation systems. In practice, the force required to shift the spool is quiet higher.
Therefore, the larger valves are often indirectly actuated in sequence.
− First, the smaller valve is actuated directly and the flow from the smaller valve is directed
to either side of the larger valve.
− The control fluid can be supplied by the same circuit or by a separate circuit. The pilot
valve pressure is usually supplied internally.
− These two valves are often incorporated as a single unit. These valves are also called as
Electro-hydraulic operated DCV.
4.3 PRESSURE CONTROL VALVE
The pressure control valves are used to protect the hydraulic components from excessive
pressure. This is one of the most important components of a hydraulic system and is
essentially required for safe operation of the system. Its primary function is to limit the
system pressure within a specified range. It reduces the system pressure and as the pressure
reduces to the set limit again the valve closes. Various types of pressure control valves are
discussed in the following sections:
m
o
1. Direct type of relief valve
.c
− Schematic of direct pressure relief valve is shown in figure 5.16. This type of valves has
two ports; one of which is connected to the pump and another is connected to the tank. It
consists of a spring chamber where poppet is placed with a spring force.
ie
h
− Generally, the spring is adjustable to set the maximum pressure limit of the system. The
poppet is held in position by combined effect of spring force and dead weight of spool.
c
e
− As the pressure exceeds this combined force, the poppet raises and excess fluid bypassed to
the reservoir (tank). The poppet again reseats as the pressure drops below the pre-set value. A
drain is also provided in the control chamber. It sends the fluid collected due to small leakage
to the tank and thereby prevents the failure of the valve.
e
T
c
A
Figure 5.16 - Pressure Relief Valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.8
Control Valves
2. Unloading Valve
− The construction of unloading valve is shown in Figure 5.17. This valve consists of a
control chamber with an adjustable spring which pushes the spool down.
− The valve has two ports: one is connected to the tank and another is connected to the pump.
The valve is operated by movement of the spool. Normally, the valve is closed and the tank
port is also closed.
m
o
.c
ie
h
Figure 5.17 - Unloading Valve
c
e
− These valves are used to permit a pump to operate at the minimum load. It works on the
same principle as direct control valve that the pump delivery is diverted to the tank when
sufficient pilot pressure is applied to move the spool.
T
The pilot pressure maintains a static pressure to hold the valve opened. The pilot pressure
holds the valve until the pump delivery is needed in the system.
e
− As the pressure is needed in the hydraulic circuit; the pilot pressure is relaxed and the spool
moves down due to the self-weight and the spring force. Now, the flow is diverted to the
hydraulic circuit.
c
A
3. Sequence valve
− The primary function of this type of valve is to divert flow in a predetermined sequence. It
is used to operate the cycle of a machine automatically. A sequence valve may be of directpilot or remote-pilot operated type.
 Schematic of the sequence valve is shown in Figure 5.18. Its construction is similar to the
direct relief valve.
− It consists of the two ports; one main port connecting the main pressure line and another
port (secondary port) is connected to the secondary circuit. The secondary port is usually
closed by the spool.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.9
Control Valves
− The pressure on the spool works against the spring force. When the pressure exceeds the
pre-set value of the spring; the spool lifts and the fluid flows from the primary port to the
secondary port.
m
o
Figure 5.18 - Sequence valve
.c
ie
h
− For remote operation; the passage used for the direct operation is closed and a separate
pressure source for the spool operation is provided in the remote operation mode.
4. Counterbalance Valve
c
e
− These valves are used in vertical presses, lift trucks, loaders and other machine tools where
position or hold suspended loads are important.
− Counterbalance valves work on the principle that the fluid is trapped under pressure until
pilot pressure overcomes the pre-set value of spring force. Fluid is then allowed to escape,
letting the load to descend under control. This valve is normally closed until it is acted upon
by a remote pilot pressure source.
e
T
c
A
Figure 5.19 - Counter Balance Valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.10
Control Valves
5. Pressure Reducing Valve
− Sometimes a part of the system may need a lower pressure. This can be made possible by
using pressure reducing valve as shown in Figure 5.20. These valves are used to limit the
outlet pressure.
− Generally, they are used for the operation of branch circuits where the pressure may vary
from the main hydraulic pressure lines.
− These are open type valve and have a spring chamber with an adjustable spring, a movable
spool as shown in figure. A drain is provided to return the leaked fluid in the spring (control)
chamber.
− A free flow passage is provided from inlet port to the outlet port until a signal from the
outlet port tends to throttle the passage through the valve. The pilot pressure opposes the
spring force and when both are balanced, the downstream is controlled at the pressure setting.
− When the pressure in the reduced pressure line exceeds the valve setting, the spool moves
to reduce the flow passage area by compressing the spring. It can be seen from the figure that
if the spring force is more, the valve opens wider and if the controlled pressure has greater
force, the valves moves towards the spring and throttles the flow.
m
o
.c
e
c
A
T
c
e
ie
h
Figure 5.20 - Pressure Reducing Valve
4.4 FLOW CONTROL VALVES
− In practice, the speed of actuator is very important in terms of the desired output and needs
to be controlled. The speed of actuator can be controlled by regulating the fluid flow.
− A flow control valve can regulate the flow or pressure of the fluid. The fluid flow is
controlled by varying area of the valve opening through which fluid passes.
− The fluid flow can be decreased by reducing the area of the valve opening and it can be
increased by increasing the area of the valve opening.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.11
Control Valves
− A very common example to the fluid flow control valve is the household tap. Figure 5.21
shows the schematic diagram of a flow control valve. The pressure adjustment screw varies
the fluid flow area in the pipe to control the discharge rate.
Figure 5.21 - Flow Control Valve
m
− The inlet pressure remains almost constant but the outlet pressure keeps on fluctuating
depending on the external load. It creates fluctuating pressure drop. Thus, the ordinary flow
control valve will not be able to maintain a constant fluid flow.
o
.c
− A pressure compensated flow control valve maintains the constant flow throughout the
movement of a spool, which shifts its position depending on the pressure.
Types of Flow Control Valves
ie
h
The flow control valves work on applying a variable restriction in the flow path. Based on the
construction; there are mainly four types viz. plug valve, butterfly valve, ball valve and
balanced valve.
1. Plug or glove valve
c
e
− The plug valve is quite commonly used valve. It is also termed as glove valve. Schematic
of plug or glove valve is shown in Figure 5.22.
e
T
− This valve has a plug which can be adjusted in vertical direction by setting flow adjustment
screw. The adjustment of plug alters the orifice size between plug and valve seat. Thus the
adjustment of plug controls the fluid flow in the pipeline.
c
A
− The characteristics of these valves can be accurately predetermined by machining the taper
of the plug. The typical example of plug valve is stopcock that is used in laboratory
glassware.
− The valve body is made of glass or teflon. The plug can be made of plastic or glass. Special
glass stopcocks are made for vacuum applications. Stopcock grease is used in high vacuum
applications to make the stopcock air-tight.
2. Butterfly valve
− A butterfly valve is shown in Figure 5.23. It consists of a disc which can rotate inside the
pipe. The angle of disc determines the restriction.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.12
Control Valves
− The resilient butterfly valve uses the flexibility of rubber and has the lowest pressure rating.
The high performance butterfly valves have a slight offset in the way the disc is positioned. It
increases its sealing ability and decreases the wear.
− For high-pressure systems, the triple offset butterfly valve is suitable which makes use of a
metal seat and is therefore able to withstand high pressure. It has higher risk of leakage on the
shut-off position and suffer from the dynamic torque effect.
− Butterfly valves are favoured because of their lower cost and lighter weight. The disc is
always present in the flow therefore a pressure drop is induced regardless of the valve
position.
m
c
e
o
.c
Figure 5.22 - Plug or glove valve
ie
h
Figure 5.23 - Butterfly valve
3. Balanced valve
T
− Schematic of a balanced valve is shown in figure 5.24. It comprises of two plugs and two
seats. The opposite flow gives little dynamic reaction onto the actuator shaft. It results in the
negligible dynamic torque effect.
e
c
− The pressure-balanced valves are used in the houses. They provide water at nearly constant
temperature to a shower or bathtub despite of pressure fluctuations in either the hot or cold
supply lines.
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.13
Control Valves
Figure 5.24 - Balanced valve
m
o
.c
ie
h
Reference Books:
1. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
2. Fluid Power with Applications by Anthony Esposito, Pearson.
e
T
c
e
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 5.14
Hydraulic Circuits
EXPERIMENT – 6
AIM – To study about basic and industrial hydraulic circuits
A hydraulic circuit is a group of components such as pumps, actuators, control valves,
conductors and fittings arranged to perform useful work. There are three important
considerations in designing a hydraulic circuit:
1. Safety of machine and personnel in the event of power failures.
2. Performance of given operation with minimum losses.
3. Cost of the component used in the circuit.
6.1 CONTROL OF A SINGLE-ACTING HYDRAULIC CYLINDER
m
o
.c
e
c
A
T
c
e
ie
h
Figure 6.1 - Control of a single-acting cylinder
− Figure 6.1 shows that the control of a single-acting, spring return cylinder using a threeway two-position manually actuated, spring offset direction-control valve (DCV). In the
spring offset mode, full pump flow goes to the tank through the pressure-relief valve (PRV).
− The spring in the rod end of the cylinder retracts the piston as the oil from the blank end
drains back into the tank. When the valve is manually actuated into its next position, pump
flow extends the cylinder.
− After full extension, pump flow goes through the relief valve. Deactivation of the DCV
allows the cylinder to retract as the DCV shifts into its spring offset mode.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.1
Hydraulic Circuits
6.2 CONTROL OF A DOUBLE-ACTING HYDRAULIC CYLINDER
The circuit diagram to control double-acting cylinder is shown in Fig. 6.2. The control of a
double-acting hydraulic cylinder is described as follows:
− When the 4/3 valve is in its neutral position (tandem design), the cylinder is hydraulically
locked and the pump is unloaded back to the tank.
m
o
.c
c
e
ie
h
Figure 6.2 - Control of a double-acting cylinder
− When the 4/3 valve is actuated into the flow path, the cylinder is extended against its load
as oil flows from port P through port A. Oil in the rod end of the cylinder is free to flow back
to the tank through the four-way valve from port B through port T.
e
T
− When the 4/3 valve is actuated into the right-envelope configuration, the cylinder retracts
as oil flows from port P through port B. Oil in the blank end is returned to the tank via the
flow path from port A to port T.
c
A
− At the ends of the stroke, there is no system demand for oil. Thus, the pump flow goes
through the relief valve at its pressure level setting unless the four-way valve is deactivated.
6.3 REGENERATIVE CYLINDER CIRCUIT
Figure 6.3 shows a regenerative circuit that is used to speed up the extending speed of a
double-acting cylinder. The pipelines to both ends of the hydraulic cylinder are connected in
parallel and one of the ports of the 4/3 valve is blocked by simply screwing a thread plug into
the port opening.
− During retraction stroke, the 4/3 valve is configured to the right envelope. During this
stroke, the pump flow bypasses the DCV and enters the rod end of the cylinder. Oil from the
blank end then drains back to the tank through the DCV.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.2
Hydraulic Circuits
− When the DCV is shifted in to its left-envelope configuration, the cylinder extends as
shown in Fig. 6.3. The speed of extension is greater than that for a regular double-acting
cylinder because the flow from the rod end regenerates with the pump flow QP to provide a
total flow rate QT.
m
o
.c
ie
h
Figure 6.3 - Regenerative circuit
6.4 DOUBLE-PUMP HYDRAULIC SYSTEM (UNLOADING CIRCUIT)
Figure 6.4 shows an application for an unloading valve. It is a circuit that uses a highpressure, low-flow pump in conjunction with a low-pressure, high-flow pump.
c
e
− A typical application is a sheet metal punch press in which the hydraulic cylinder must
extend rapidly over a great distance with low-pressure but high-flow requirements. This
occurs under no load.
e
T
− However during the punching operation for short motion, the pressure requirements are
high, but the cylinder travel is small and thus the flow requirements are low. The circuit in
Fig. 6.4 eliminates the necessity of having a very expensive high-pressure, high-flow pump.
c
A
− When the punching operation begins, the increased pressure opens the unloading valve to
unload the low-pressure pump. The purpose of relief valve is to protect the high-pressure
pump from over pressure at the end of cylinder stroke and when the DCV is in its springcentered mode.
− The check valve protects the low-pressure pump from high pressure, which occurs during
punching operation, at the ends of the cylinder stroke and when the DCV is in its springcentered mode.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.3
Hydraulic Circuits
m
Figure 6.4 - Double-pump circuit
6.5 COUNTERBALANCE VALVE APPLICATION
e
T
c
e
o
.c
ie
h
c
A
Figure 6.5 - Counterbalance valve in circuit
− A counterbalance valve (Fig. 6.5) is applied to create a back pressure or cushioning
pressure on the underside of a vertically moving piston to prevent the suspended load from
free falling because of gravity while it is still being lowered.
6.5.1 Valve Operation (Lowering)
− The pressure setting on the counterbalance valve is set slightly higher than the pressure
required to prevent the load from free falling. Due to this back pressure in line A, the actuator
piston must force down when the load is being lowered.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.4
Hydraulic Circuits
− This causes the pressure in line A to increase, which raises the spring-opposed spool, thus
providing a flow path to discharge the exhaust flow from line A to the DCV and then to the
tank.
− The spring-controlled discharge orifice maintains back pressure in line A during the entire
downward piston stroke.
6.5.2 Valve Operation (Lifting)
As the valve is normally closed, flow in the reverse direction (from port B to port A) cannot
occur without a reverse free-flow check valve.
− When the load is raised again, the internal check valve opens to permit flow for the
retraction of the actuator.
6.5.3 Valve Operation (Suspension)
When the valve is held in suspension, the valve remains closed. Therefore, its pressure setting
must be slightly higher than the pressure caused by the load. Spool valves tend to leak
internally under pressure. This makes it advisable to use a pilot-operated check valve in
addition to the counterbalance valve if a load must be held in suspension for a prolonged
time.
m
o
.c
6.6 HYDRAULIC CYLINDER SEQUENCING CIRCUITS
Hydraulic cylinders can be operated sequentially using a sequence valve. Figure 6.6 shows
that two sequence valves are used to sequence the operation of two double-acting cylinders.
ie
h
− When the DCV is actuated to its right-envelope mode, the bending cylinder (B) retracts
fully and then the clamp cylinder (A) retracts.
c
e
− This sequence of cylinder operation is controlled by sequence valves. This hydraulic circuit
can be used in a production operation such as drilling.
− Cylinder A is used as a clamp cylinder and cylinder B as a drill cylinder.
T
− Cylinder A extends and clamps a work piece. Then cylinder B extends to drive a spindle to
e
drill a hole. Cylinder B retracts the drill spindle and then cylinder A retracts to release the
work piece for removal.
c
6.7 AUTOMATIC CYLINDER RECIPROCATING SYSTEM
A
The hydraulic circuit shown in Fig. 6.7 produces continuous reciprocation of a double-acting
cylinder using two sequence valves. Each sequence valve senses the completion of stroke by
the corresponding build-up pressure. Each check valve and the corresponding pilot line
prevent the shifting of the four-way valve until the particular stroke of the cylinder is
completed.
− The check valves are needed to allow pilot oil to leave either end of the DCV while the pilot
pressure is applied to the opposite end. This permits the spool of the DCV to shift as required.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.5
Hydraulic Circuits
m
Figure 6.6 - Sequencing circuit
e
T
c
e
o
.c
ie
h
c
A
Figure 6.7 - Automatic Cylinder Reciprocating System
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.6
Hydraulic Circuits
6.8 CYLINDER SYNCHRONIZING CIRCUITS
In industry, there are instances when a large mass must be moved, and it is not feasible to
move it with just one cylinder. In such cases we use two or more cylinders to prevent a
moment or moments that might distort and damage the load. For example, in press used for
moulding and shearing parts, the platen used is very heavy. If the platen is several meter
wide, it has to be of very heavy construction to prevent the damage when it is pressed down
by a single cylinder in the middle. It can be designed with less material if it is pressed down
with two or more cylinders. These cylinders must be synchronized. There are two ways that
can be used to synchronize cylinders: Parallel and series.
6.8.1 Cylinders in Parallel
Figure 6.8 shows a hydraulic circuit in which two cylinders are arranged in parallel. When
the two cylinders are identical, the loads on the cylinders are identical, and then extension
and retraction are synchronized. If the loads are not identical, the cylinder with smaller load
extends first. Thus, the two cylinders are not synchronized. Practically, no two cylinders are
identical, because of packing (seals) friction differences. This prevents cylinder
synchronization for this circuit.
m
o
6.8.2 Cylinders in Series
.c
During the extending stroke of cylinders, fluid from the pump is delivered to the blank end of
cylinder 1. As cylinder 1 extends, fluid from its rod end is delivered to the blank end of
cylinder 2 causing the extension of cylinder 2. As cylinder 2 extends, fluid from its rod end
reaches the tank.
ie
h
− For two cylinders to be synchronized, the piston area of cylinder 2 must be equal to the
c
e
difference between the areas of piston and rod for cylinder 1. Thus, applying the continuity
equation,
Qout (Cylinder 1) = Qin (Cylinder 2)
We get
e
T
c
(Ap1 – Ar1) v1 = Ap2 v2
For synchronization, v1 = v2. Therefore,
A
(Ap1 – Ar1) = Ap2
(6.8.1)
− The pump must deliver a pressure equal to that required for the piston of cylinder 1 by itself
to overcome loads acting on both extending cylinders. We know that the pressure acting at
the blank end of cylinder 2 is equal to the pressure acting at the rod end of cylinder 1.
Forces acting on cylinder 1 give
p1Ap1 – p2 (Ap1 –Ar1) = F1
Forces acting on cylinder 2 give
P2Ap2 – p2 (Ap2 –Ar2) = F2
Using Eq. (6.8.1) and noting that p3 = 0 (it is connected to the tank), we have
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.7
Hydraulic Circuits
p1Ap1 – p2Ap2 = F1
(6.8.2
m
p2Ap2 – 0 = F2
Now, Eq. (6.8.2) + Eq. (6.8.3) gives
o
.c
Figure 6.8 - Cylinders in parallel and series
ie
h
p1Ap1 = F1 + F2
(6.8.3)
(6.8.4)
If Eqs. (6.8.1) and (6.8.4) are met in a hydraulic circuit, the cylinders hooked in series operate
in synchronization.
c
e
6.9 SPEED CONTROL OF A HYDRAULIC CYLINDER
− The speed control of a hydraulic cylinder circuit can be done during the extension stroke
T
using a flow-control valve (FCV). This is done on a meter-in circuit and meter-out circuit
as shown in Fig. 6.9.
e
c
− Refer to Fig. 6.9 (a). When the DCV is actuated, oil flows through the FCV to extend the
cylinder. The extending speed of the cylinder depends on the FCV setting. When the DCV is
deactivated, the cylinder retracts as oil from the cylinder passes through the check valve.
Thus, the retraction speed of a cylinder is not controlled.
A
− Figure 6.9 (b) shows meter-out circuit; when DCV is actuated, oil flows through the rod end
to retract the cylinder.
6.9.1 Meter-In Versus Meter-Out Flow-Control Valve Systems
− In Section 6.9, the FCV is placed in the line leading to the inlet port of the cylinder. Thus, it
is called the meter-in control of speed. Meter-in flow controls the oil flow rate into the
cylinder.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.8
Hydraulic Circuits
− A meter-out flow control system is one in which the FCV is placed in the outlet line of the
hydraulic cylinder. Thus, a meter-out flow control system controls the oil flow rate out of the
cylinder.
− Meter-in systems are used primarily when the external load opposes the direction of motion
of the hydraulic cylinder. When a load is pulled downward due to gravity, a meter-out system
is preferred. If a meter-in system is used in this case, the load would drop by pulling the
piston rod, even if the FCV is completely closed.
− One drawback of a meter-out system is the excessive pressure build-up in the rod end of the
cylinder while it is extending. In addition, an excessive pressure in the rod end results in a
large pressure drop across the FCV. This produces an undesirable effect of a high heat
generation rate with a resulting increase in oil temperature.
m
o
.c
e
T
c
e
ie
h
c
A
Figure 6.9 - Speed control of cylinders: (a) Meter in and (b) meter out.
6.10 Fail-Safe Circuits
Fail-safe circuits are those designed to prevent injury to the operator or damage to the
equipment. In general, they prevent the system from accidentally falling on an operator and
also prevent overloading of the system. In following sections we shall discuss two fail-safe
circuits: One is protection from inadvertent cylinder extension and other is fail-safe overload
protection.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.9
Hydraulic Circuits
1. Protection from inadvertent cylinder extension:
− Figure 6.10 shows a fail-safe circuit that is designed to prevent the cylinder from
accidentally falling in the event when a hydraulic line ruptures or a person inadvertently
operates the manual override on the pilot-actuated DCV when the pump is not working.
− To lower the cylinder, pilot pressure from the blank end of piston must pilot open the check
valve to allow oil to return through the DCV to the tank.
− This happens when the push button is actuated to permit the pilot pressure actuation of
DCV or when the DCV is directly manually actuated when the pump operates.
− The pilot-operated DCV allows free flow in the opposite direction to retract the cylinder
when this DCV returns to its offset mode.
2. Fail-Safe System with Overload Protection:
− Figure 6.11 shows a fail-safe system that provides overload protection for system
components. The DCV V1 is controlled by the push-button three-way valve V2.
m
− When the overload valve V3 is in its spring offset mode, it drains the pilot line of valve V1.
o
If the cylinder experiences excessive resistance during the extension stroke, sequence valve
V4 pilot-actuates overload valve V3.
.c
− This drains the pilot line of valve V1 causing it to return to its spring offset mode. If a
ie
h
person then operates the push-button valve V2 nothing happens unless overload valve V3 is
manually shifted into its blocked-port configuration.
− Thus, the system components are protected against excessive pressure due to an excessive
cylinder load during its extension stroke.
e
T
c
e
c
A
Figure 6.10 - Fail-safe circuits – Inadvertent
Cylinder Extension
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Figure 6.11 - Fail-safe circuits Overload Protection.
Prepared By: Jainik Makwana
Page 6.10
Hydraulic Circuits
Reference Books:
1. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
2. The Analysis & Design of Pneumatic Systems by B. W. Anderson, John Wiley
m
o
.c
e
T
c
e
ie
h
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 6.11
Basics of Pneumatic System
EXPERIMENT – 7
AIM – To study about basic pneumatic system and its component
7.1 PNEUMATICS AND ITS MEANING
− Pneumatics is application of compressed air (pressurized air) to power machine or control
or regulate machines. Simply put, Pneumatics may be defined as branch of engineering
science which deals with the study of the behaviour and application of compressed air.
− Any gas can be used in pneumatic system but air is the most usual, for obvious reasons.
Exceptions are most likely to occur on aircraft and space vehicles where an inert gas such as
nitrogen is preferred or the gas is one which is generated on board. Pure nitrogen may be used
if there is a danger of combustion in a work environment. In Pneumatic control, compressed
air is used as the working medium, normally at a pressure from 7 bar to 8 bar. Using
Pneumatic
m
o
.c
− Control, maximum force up to 50 kN can be developed. Actuation of the controls can be
manual, Pneumatic or Electrical actuation. Signal medium such as compressed air at pressure
of 1-2 bar can be used [Pilot operated Pneumatics] or Electrical signals [D.C or A.C source24V – 230V] can be used [Electro pneumatics]
ie
h
Table 7.1 - The advantages and disadvantages of compressed air
Advantages of compressed air
c
e
Air is available in unlimited quantities.
Compressed air is easily conveyed in
pipelines even over longer distances
e
T
Disadvantages of compressed air
Compressive air is relatively expensive
means of conveying energy
The higher costs are, however. Largely
compensated by the cheaper elements.
Simpler and more compact equipment
Compressed
air
requires
good
conditioning. No dirt or moisture
residues may be contained in it. Dirt and
dust leads to wear on tools and
equipment
It is not possible to achieve uniform and
constant piston speeds( air is
compressible)
Compressed air is economical ony up to
certain force expenditure. Owing to the
commonly used pressure of 7 bar and
limit is about 20 to 50 kN, depending on
the travel and the speed. If the force
which is required exceeds this level,
hydraulics is preferred
The exhaust is loud. As the result of
c
Compressed air can be stored
A
Compressed air need not be returned. It
can be vented to atmosphere after it has
performed work
Compressed air is insensitive to
temperature fluctuation. This ensures
reliable operation even in extreme
temperature conditions
Compressed air is clean. This is
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 7.1
Basics of Pneumatic System
especially
important
in
food, intensive
development
work
on
pharmaceutical,
textile,
beverage materials for silencing purposes, this
industries
problems has however now largely been
solved
Operating elements for compressed air The oil mist mixed with the air for
operation are of simple and inexpensive lubricating the equipment escapes with
construction.
the exhaust to atmosphere.
Compressed air is fast. Thus, high Air due to its low conductivity , cannot
operational speed can be attained.
dissipate heat as much as hydraulic fluid
Air cannot seal the fine gaps between
Speeds and forces of the pneumatics
the moving parts unlike hydraulic
elements can be infinitely adjusted
system
Tools and operating elements are
Air is not a good lubricating medium
overload proof. Straight line movement
unlike hydraulic fluid.
can be produced directly
7.2 APPLICATIONS OF PNEUMATICS
m
Some of the Industrial applications of pneumatics are listed in the Table 7.2.
Table 7.2 - Industrial applications of Pneumatics
Material
Handling
Clamping
Shifting
positioning
Orienting
Feeding
Ejection
Braking
Bonding
Locking
Packaging
Feeding
Sorting
stacking
e
T
Manufacturing
.c
Aircraft
Cement plants
chemical plants
Coal mines
Cotton mills
Dairies
Forge shops
Machine tools
Door or chute
control
Turning and
inverting parts
ie
h
Drilling
Turning
Milling
Sawing
Finishing
Forming
Quality Control
Stamping
Embossing
Filling
c
e
o
Other
applications
c
7.3 PROPERTIES OF AIR
A
Composition:
− Air is a mechanical mixture of gases containing by volume, approximately 78 % of
nitrogen and 21 % of oxygen, and about 1 % of other gases, including argon and carbon
dioxide. Water being the most important remaining ingredient as far as pneumatics is
concerned.
− Air is colorless, odorless, tasteless, and compressible and has weight. Air has a great
affinity with water and unless specifically dried, contains considerable quantities of water
vapour, sometimes as much as 1% by weight. Life on earth depends on air for survival and
man harness its forces to do useful work. Table 1.3 gives the physical properties of air
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 7.2
Basics of Pneumatic System
Table 7.3 - Properties of air
Property
Molecular weight
Density of air at 15 and 1
bar
Boiling point at 1 bar
Freezing point at 1 bar
Gas constant
Value
28.97 kg/kmol
1.21 kg/m3
191 to -194
-212 to -217
287.9 J/kg K
Free air and Standard air
In pneumatics, the existence of the following two conditions of atmospheric air is well
accepted
• Free air: Air at the atmospheric condition at the point where the compressor is located is
defined as free air. Free air will vary with atmospheric conditions like altitude, pressure and
temperature.
m
o
• Standard air: It is also called normal air. It is defined as the air at sea level conditions
(1.01324 bar as per ISO –R554 and 20 and Relative humidity of 37%). The condition of
normal atmosphere is used as a basis for getting average values for compressor delivery
volumes, efficiencies and operating characteristics.
.c
ie
h
Atmospheric pressure, Gauge pressure and Absolute pressure
− Air has mass and exerts a pressure on the surface of the earth. A barometer consisting of an
inverted tube close at the top will support a column of mercury at exactly 770 mm at sea level
when measured at standard conditions.
c
e
− Pressure above one atmosphere (~ 1 bar) are positive, whereas the pressure below one
atmosphere cause a vacuum to be formed.
T
− Both positive pressures and vacuum pressures have useful purposes in pneumatics. Vacuum
measurement is usually given a mm of mercury and then converted into the holding force for
such devices such as suction pads and cylinders with a specified diameter.
e
c
Atmospheric pressure:
A
− The earth is surrounded by air. Since air has weight it can exert a pressure on the earth’s
surface. The weight of the column of air on one square meter of earth’s surface is known as
atmospheric pressure or reference pressure.
− The atmospheric pressure varies slightly from day to day. In pneumatic circuit calculations,
standard atmospheric pressure is taken as 101.325 kPa. (14.7 psia)(770 mm of Hg). The
atmospheric pressure is measured using barometer.
− Atmospheric pressure = Density x Acceleration due to gravity x height of barometer
column (usually mercury)
P atm = ρ g h
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 7.3
Basics of Pneumatic System
Gauge Pressure:
− In pneumatic application, pressure is measured using pressure gage and pressure gauges are
calibrated to indicate the pressure above that of the Atmospheric pressure. Gauge pressure
refers to pressure indicated by pressure gauge.
Absolute pressure:
− Refers to the true or total pressure.
Absolute pressure = Atmospheric pressure + Gauge pressure.
− Calculations involving formulae associated with the Gas laws must be made with absolute
pressure. Figure 7.1 shows the difference between the gauge and absolute pressure.
m
o
.c
c
e
ie
h
Figure 7.1 - Difference between absolute and gauge pressure
T
7.4 BASIC COMPONENTS OF PNEUMATIC SYSTEM
Important components of a pneumatic system are shown in figure 7.2.
e
c
a) Air filters: These are used to filter out the contaminants from the air.
b) Compressor: Compressed air is generated by using air compressors. Air compressors are
either diesel or electrically operated. Based on the requirement of compressed air, suitable
capacity compressors may be used.
A
c) Air cooler: During compression operation, air temperature increases. Therefore coolers
are used to reduce the temperature of the compressed air.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 7.4
Basics of Pneumatic System
Figure 7.2 - Components of a pneumatic system
m
o
d) Dryer: The water vapor or moisture in the air is separated from the air by using a dryer.
.c
e) Control Valves: Control valves are used to regulate, control and monitor for control of
direction flow, pressure etc.
ie
h
f) Air Actuator: Air cylinders and motors are used to obtain the required movements of
mechanical elements of pneumatic system.
g) Electric Motor: Transforms electrical energy into mechanical energy. It is used to drive
the compressor.
c
e
h) Receiver tank: The compressed air coming from the compressor is stored in the air
receiver.
e
T
c
Reference Books:
1. Basic Pneumatic Systems, Principle and Maintenance by S R Majumdar, McGrawHill.
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 7.5
Pneumatic Compressor
EXPERIMENT – 8
AIM – To study about pneumatic compressors and its characteristics
8.1 COMPRESSOR
− It is a mechanical device which converts mechanical energy into fluid energy. The
compressor increases the air pressure by reducing its volume which also increases the
temperature of the compressed air.
− The compressor is selected based on the pressure it needs to operate and the delivery
volume.
− The compressor can be classified into two main types
a. Positive displacement compressors and
m
b. Dynamic displacement compressor
o
− Positive displacement compressors include piston type, vane type, diaphragm type and
.c
screw type.
Piston compressors
e
T
c
e
ie
h
c
A
Figure 8.1 - Single acting piston compressor
− Piston compressors are commonly used in pneumatic systems. The simplest form is single
cylinder compressor (Figure 8.1). It produces one pulse of air per piston stroke.
− As the piston moves down during the inlet stroke the inlet valve opens and air is drawn into
the cylinder. As the piston moves up the inlet valve closes and the exhaust valve opens which
allows the air to be expelled. The valves are spring loaded.
− The single cylinder compressor gives significant amount of pressure pulses at the outlet
port. The pressure developed is about 3-40 bar.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.1
Pneumatic Compressor
Double acting compressor
− The pulsation of air can be reduced by using double acting compressor as shown in Figure
8.2. It has two sets of valves and a crosshead.
− As the piston moves, the air is compressed on one side whilst on the other side of the
piston, the air is sucked in. Due to the reciprocating action of the piston, the air is compressed
and delivered twice in one piston stroke. Pressure higher than 30bar can be produced.
Multistage compressor
− As the pressure of the air increases, its temperature rises. It is essential to reduce the air
temperature to avoid damage of compressor and other mechanical elements. The multistage
compressor with intercooler in-between is shown in Figure 8.3.
− It is used to reduce the temperature of compressed air during the compression stages. The
inter-cooling reduces the volume of air which used to increase due to heat.
m
o
.c
c
e
ie
h
Figure 8.2 - Double acting piston compressor
e
T
c
A
Figure 8.3 - Multi-stage compressor
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.2
Pneumatic Compressor
− The compressed air from the first stage enters the intercooler where it is cooled. This air is
given as input to the second stage where it is compressed again.
− The multistage compressor can develop a pressure of around 50 bar.
Combined two stage compressors
− In this type, two-stage compression is carried out by using the same piston (Fig. 8.4).
Initially when the piston moves down, air is sucked in through the inlet valve.
− During the compression process, the air moves out of the exhaust valve into the intercooler.
As the piston moves further the stepped head provided on the piston moves into the cavity
thus causing the compression of air. Then, this is let out by the exhaust port.
m
o
.c
c
e
ie
h
Figure 8.4 - Combined to stage compressor
Diaphragm compressor
e
T
c
A
Figure 8.5 - Diaphragm compressor
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.3
Pneumatic Compressor
− These are small capacity compressors. In piston compressors the lubricating oil from the
pistons walls may contaminate the compressed air.
− The contamination is undesirable in food, pharmaceutical and chemical industries. For such
applications diaphragm type compressor can be used. Figure 8.8 shows the construction of
Diaphragm compressor.
− The piston reciprocates by a motor driven crankshaft. As the piston moves down it pulls the
hydraulic fluid down causing the diaphragm to move along and the air is sucked in.
− When the piston moves up the fluid pushes the diaphragm up causing the ejection of air
from the outlet port. Since the flexible diaphragm is placed in between the piston and the air
no contamination takes place.
Screw compressor
− Piston compressors are used when high pressures and relatively low volume of air is
needed. The system is complex as it has many moving parts. For medium flow and pressure
applications, screw compressor can be used. It is simple in construction with less number of
moving parts.
m
o
− The air delivered is steady with no pressure pulsation. It has two meshing screws. The air
.c
from the inlet is trapped between the meshing screws and is compressed. The contact
between the two meshing surface is minimum, hence no cooling is required.
ie
h
− These systems are quite in operation compared to piston type. The screws are synchronized
by using external timing gears.
e
T
c
e
c
A
Figure 8.6 - Screw compressor
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.4
Pneumatic Compressor
Rotary vane compressors
− The principle of operation of vane compressor is similar to the hydraulic vane pump. Figure
8.7 shows the working principle of Rotary vane compressor. The unbalanced vane
compressor consists of spring loaded vanes seating in the slots of the rotor.
− The pumping action occurs due to movement of the vanes along a cam ring. The rotor is
eccentric to the cam ring.
− As the rotor rotates, the vanes follow the inner surface of the cam ring. The space between
the vanes decreases near the outlet due to the eccentricity. This causes compression of the air.
These compressors are free from pulsation. If the eccentricity is zero no flow takes place.
Liquid ring vane compressor
− Liquid ring vane compressor is a variation of vane compressors. Figure 8.8 shows the
construction of Liquid ring compressor. The casing is filled with liquid up to rotor center.
The air enters the compressor through the distributor fixed to the compressor.
m
− During the impeller rotation, the liquid will be centrifuged along the inner ring of the casing
to form the liquid ring.
o
.c
T
c
e
ie
h
Figure 8.7 - Rotary vane compressor
e
− There are two suction and discharge ports provided in the distributor. During the first
c
quarter of cycle, the air is sucked in both suction chambers of the casing and during the
second quarter of the cycle, the air is compressed and pushed out through the two discharge
ports.
A
− During the third and fourth quarters of the cycle, the process is repeated. This type of
compressor has no leakage and has minimal friction. For smooth operation, the rotation speed
should be about 3000 rpm. The delivery pressure is low (about 5 bar).
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.5
Pneumatic Compressor
Figure 8.8 - Liquid ring compressor
Lobe compressor
m
− The lobe compressor is used when high delivery volume but low pressure is needed. It
consists of two lobes with one being driven and the other driving.
o
− Figure 8.9 shows the construction and working of Lobe compressor. It is similar to the Lobe
.c
pump used in hydraulic systems.
− The operating pressure is limited by leakage between rotors and housing. As the wear
ie
h
increases during the operation, the efficiency falls rapidly.
e
T
c
e
c
A
Figure 8.9 - Lobe compressor
8.2 FILTER, REGULATOR AND LUBRICATION (FRL) UNIT
Filter
− To prevent any damage to the compressor, the contaminants present in the air need to be
filtered out. This is done by using inlet filters. These can be dry or wet filters.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.6
Pneumatic Compressor
− Dry filters use disposable cartridges. In the wet filter, the incoming air is passed through an
oil bath and then through a fine wire mesh filter.
− Dirt particles cling to the oil drops during bubbling and are removed by wire mesh as they
pass through it. In the dry filter the cartridges are replaced during servicing. The wet filters
are cleaned using detergent solution.
Lubricators
− The compressed air is first filtered and then passed through a lubricator in order to form a
mist of oil and air to provide lubrication to the mating components. Figure 8.10 shows the
schematic of a typical lubricator. The principle of working of venture meter is followed in the
operation of lubricator.
− The compressed air from the dryer enters in the lubricator. Its velocity increases due to a
pressure differential between the upper and lower changer (oil reservoir). Due to the low
pressure in the upper chamber the oil is pushed into the upper chamber from the oil reservoir
through a siphon tube with check valve.
m
o
.c
e
c
A
T
c
e
ie
h
Figure 8.10 - Air lubricator
Pressure regulation
In pneumatic systems, during high velocity compressed air flow, there is flow-dependent
pressure drop between the receiver and load (application). Therefore the pressure in the
receiver is always kept higher than the system pressure. At the application site, the pressure is
regulated to keep it constant. There are three ways to control the local pressure, these are
shown in Figure 8.11.
− In the first method, load X vents the air into atmosphere continuously. The pressure
regulator restricts the air flow to the load, thus controlling the air pressure. In this type of
pressure regulation, some minimum flow is required to operate the regulator. If the load is a
dead end type which draws no air, the pressure in the receiver will rise to the manifold
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.7
Pneumatic Compressor
pressure. These type of regulators are called as ‘non-relieving regulators’, since the air must
pass through the load.
− In the second type, load Y is a dead end load. However the regulator vents the air into
atmosphere to reduce the pressure. This type of regulator is called as ‘relieving regulator’.
− The third type of regulator has a very large load Z. Therefore its requirement of air volume
is very high and can’t be fulfilled by using a simple regulator. In such cases, a control loop
comprising of pressure transducer, controller and vent valve is used. Due to large load the
system pressure may rise above its critical value. It is detected by a transducer. Then the
signal will be processed by the controller which will direct the valve to be opened to vent out
the air. This technique can be also be used when it is difficult to mount the pressure
regulating valve close to the point where pressure regulation is needed.
m
o
.c
e
c
T
c
e
ie
h
Figure 8.11 - Types of pressure regulation
A
Reference Books:
1. Basic Pneumatic Systems, Principle and Maintenance by S R Majumdar, McGrawHill.
2. Hydraulic and Pneumatic Controls: Understanding made Easy, K.Shanmuga
Sundaram, S.Chand & Co Book publishers, New Delhi, 2006 (Reprint 2009)
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 8.8
Pneumatic Valves
EXPERIMENT – 9
AIM – To study about special valves used in pneumatic circuit
9.1 VALVES
Valve are defined as devices to control or regulate the commencement, termination and
direction and also the pressure or rate of flow of a fluid under pressure which is delivered by
a compressor or vacuum pump or is stored in a vessel.
Values of one sort or another, perform three main function in pneumatic installation
− They control the supply of air to power units, example cylinders
− They provide signal which govern the sequence of operation
m
− They act as interlock and safety devices
o
− The type of valve used is of little importance in a pneumatic control for most part. What is
important is the function that can be initiated with the valves, its mode of actuation and line
connection size, the last named characteristics also determining the flow size of the valve.
.c
ie
h
− Valves used in pneumatics mainly have a control function that is when they act on some
process, operation or quantity to be stopped. A control function requires control energy, it
being desirable to achieve the greatest possible effect with the least effort. The form of
control energy will be dictated by the valve’s mode of actuation and may be manual,
mechanical, electrical hydraulic or pneumatic.
c
e
− Valve available for pneumatic control can be classified into four principal groups according
to their function:
T
1. Direction control valve (Same as used in hydraulics. Range of working pressure is less)
2. Non return valves
e
c
3. Flow control valves (Same as used in hydraulics. Range of working pressure is less)
A
4. Pressure control valves (Same as used in hydraulics. Range of working pressure is less)
Non return valves
− Non return valves permit flow of air in one direction only, the other direction through the
valve being at all times blocked to the air flow. Mostly the valves are designed so that the
check is additionally loaded by the downstream air pressure, thus supporting the non-return
action.
− Among the various types of non-return valves available, those preferentially employed in
pneumatic controls are as follows
A) Check valve
B) Shuttle valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 9.1
Pneumatic Valves
C) Restrictor check valve
D) Quick exhaust valve
E) Two pressure valve
A. Check valve
− The simplest type of non-return valve is the check valve (Figure 9.1) which completely
blocks air flow in one direction while permitting flow in the opposite direction with minimum
pressure loss across the valve.
− As soon as the inlet pressure in the direction of free flow develops a force greater than that
of the internal spring, the check is lifted clear of the valve seat. The check in such valve may
be plug, ball, plate or diaphragm.
B. Shuttle valve
− It is also known as a double control valve or double check valve. A shuttle valve has two
inlets and one outlet. At any one time, flow is shut off in the direction of whichever inlet is
unloaded and is open from the loaded inlet to the outlet (Figure 9.2).
m
o
− A shuttle valve may be installed, for example, when a power unit (cylinder) or control unit
(valve) is to be actuated from two points, which may be remote from one other.
.c
e
T
c
e
ie
h
c
A
Figure 9.1 - Check valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 9.2
Pneumatic Valves
Figure 9.2 - Pneumatic Shuttle valve
C. Quick Exhaust Valves
− A quick exhaust valve is a typical shuttle valve. The quick exhaust valve is used to exhaust
the cylinder air quickly to atmosphere. Schematic diagram of quick exhaust valve is shown in
Figure 9.3. In many applications especially with single acting cylinders, it is a common
practice to increase the piston speed during retraction of the cylinder to save the cycle time.
m
o
− The higher speed of the piston is possible by reducing the resistance to flow of the
exhausting air during the motion of cylinder. The resistance can be reduced by expelling the
exhausting air to the atmosphere quickly by using Quick exhaust valve.
.c
ie
h
− The construction and operation of a quick exhaust valve is shown in Figure 9.3. It consist
of a movable disc (also called flexible ring) and three ports namely, Supply port 1, which is
connected to the output of the final control element (Directional control valve). The Output
port, 2 of this valve is directly fitted on to the working port of cylinder. The exhaust port, 3 is
left open to the atmosphere
e
T
c
e
c
A
Figure 9.3 - Functional diagram of quick exhaust valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 9.3
Pneumatic Valves
Forward Motion: During forward movement of piston, compressed air is directly admitted
behind the piston through ports 1 and 2 Port 3 is closed due to the supply pressure acting on
the diaphragm. Port 3 is usually provided with a silencer to minimize the noise due to
exhaust.
Return Motion: During return movement of piston, exhaust air from cylinder is directly
exhausted to atmosphere through opening 3 (usually larger and fitted with silencer) .Port 2 is
sealed by the diaphragm. Thus exhaust air is not required to pass through long and narrow
passages in the working line and final control valve
D. Two Pressure Valve
− This valve is the pneumatic AND valve. It is also derivate of Non Return Valve. A two
pressure valve requires two pressurised inputs to allow an output from itself. The cross
sectional views of two pressure valve in two positions are given in Figure 9.4.
− As shown in the figure, this valve has two inputs 12 and 14 and one output 2. If the
compressed air is applied to either 12 or input 14, the spool moves to block the flow, and no
signal appears at output 2. If signals are applied to both the inputs 12 and 14, the compressed
air flows through the valve, and the signal appears at output 2.
m
o
.c
T
c
e
ie
h
Figure 9.4 - Two pressure valve
e
c
A
Reference Books:
1. Basic Pneumatic Systems, Principle and Maintenance by S R Majumdar, McGrawHill.
2. Hydraulic and Pneumatic Controls: Understanding made Easy, K.Shanmuga
Sundaram, S.Chand & Co Book publishers, New Delhi, 2006 (Reprint 2009)
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 9.4
Pneumatic Circuits
EXPERIMENT – 10
AIM – To study about different basic and industrial pneumatic circuits
10.1 INTRODUCTION
Pneumatic control systems can be designed in the form of pneumatic circuits. A pneumatic
circuit is formed by various pneumatic components, such as cylinders, directional control
valves, flow control valves, pressure regulator, signal processing elements such as shuttle
valve, two pressure valve etc. Pneumatic circuits have the following functions

To control the entry and exit of compressed air in the cylinders.

To use one valve to control another valve

To control actuators or any other pneumatic devices
10.2 SINGLE ACTING CYLINDER CONTROL
m
e
T
c
e
o
.c
10.2.1 Direct control of single acting cylinder
ie
h
c
A
Figure 10.1 - Direct control of a single acting cylinder
− Pneumatic cylinders can be directly controlled by actuation of final directional control valve
(Figure 10.1). These valves can be controlled manually or electrically. This circuit can be
used for small cylinders as well as cylinders which operates at low speeds where the flow rate
requirements are less.
− When the directional control valve is actuated by push button, the valve switches over to the
open position, communicating working source to the cylinder volume. This results in the
forward motion of the piston. When the push button is released, the reset spring of the valve
restores the valve to the initial position [closed].
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.1
Pneumatic Circuits
− The cylinder space is connected to exhaust port there by piston retracts either due to spring
or supply pressure applied from the other port.
Example 1: A small single acting cylinder is to extend and clamp a work piece when a push
button is pressed. As long as the push button is activated, the cylinder should remain in the
clamped position. If the push button is released, the clamp is to retract. Use additional start
button. Schematic diagram of the setup is shown in Figure 10.2
Figure 10.2
m
Solution
o
The control valve used for the single acting cylinder is the 3/2 way valve. In this case, since
the cylinder is of small capacity, the operation can be directly controlled by a push button 3/2
way directional control valve with spring return.
.c
e
T
c
e
ie
h
c
A
Figure 10.3
When start button and 3/2 NC valve is operated, cylinder moves forward to clamp the work
piece. When start button and 3/2 way valve is released cylinder comes back to the retracted
position as shown in Figure 10.3.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.2
Pneumatic Circuits
10.2.2 Indirect control of single acting cylinder
− This type of circuit (Figure 10.4) is suitable for large single cylinders as well as cylinders
operating at high speeds. The final pilot control valve is actuated by normally closed 3/2 push
button operated valve. The final control valves handle large quantity of air.
− When the push button is pressed, 3/2 normally closed valve generate a pilot signal 12 which
controls the final valve thereby connecting the working medium to piston side of the cylinder
so as to advance the cylinder.
− When the push button is released, pilot air from final valve is vented to atmosphere through
3/2 NC – DCV.
m
o
.c
c
e
ie
h
Figure 10.4 - Indirect control of a single acting cylinder
− The signal pressure required can be around 1-1.5 bar. The working pressure passing through
the final control valve depends on the force requirement which will be around 4-6 bar.
T
− Indirect control as permits processing of input signals. Single piloted valves are rarely used
e
in applications where the piston has to retract immediately on taking out the set pilot signal.
c
Example 2: A large single acting cylinder is to extend and clamp a work piece when a push
button is pressed. As long as the push button is activated, the cylinder should remain in the
clamped position. If the push button is released, the clamp is to retract. Use additional start
button.
A
The control valve used for the single acting cylinder is the 3/2 way valve. In this case, since
the cylinder is of large capacity, the operation cannot be directly controlled by a push button
3/2 way directional control valve with spring return. Indirect control is to be used as shown in
the Figure 10.5
Valve 2 is a small capacity valve which controls the large capacity valve 3. When the valve 2
is unactuated the cylinder is in the retracted condition. When the valve 2 is actuated the
cylinder is in the extended position to clamp the work piece.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.3
Pneumatic Circuits
m
o
.c
Figure 10.5 - Indirect control of single acting cylinder
ie
h
10.2.3 Control of single acting cylinder using “or” valve (Shuttle valve)
− Shuttle valve is also known as double control valve or double check valve. A shuttle valve
has two inlets and one outlet (Figure 10.6). At any one time, flow is shut off in the direction
of whichever inlet is unloaded and is open from the loaded inlet to the outlet. This valve is
also called an OR valve.
c
e
− A shuttle valve may be installed for example, when the cylinder or valve is to be actuated
T
from two points, which may be remote from one another.
e
c
A
Figure 10.6 - Shuttle valve (OR valve)
− The single acting cylinder in Figure 10.10 can be operated by two different circuits.
Examples include manual operation and relying on automatic circuit signals, that is, when
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.4
Pneumatic Circuits
either control valve 1 or control valve 2 is operated, the cylinder will work. Therefore, the
circuit in Figure 10.10 possesses the OR function.
Figure 10.10 - Control of a single acting cylinder using OR valve
m
o
10.2.4 Control of single acting cylinder using “and” valve (Non Return Valve)
.c
− This valve is the pneumatic AND valve. It is also derivate of Non Return Valve. A two
pressure valve requires two pressurised inputs to allow an output from itself. The cross
sectional views of two pressure valve in two positions are given in Figure 10.8.
ie
h
− As shown in the Figure 10.8, this valve has two inputs 12 and 14 and one output 2. If the
compressed air is applied to either 12 or input 14, the spool moves to block the flow, and no
signal appears at output 2. If signals are applied to both the inputs 12 and 14, the compressed
air flows through the valve, and the signal appears at output 2.
e
T
c
e
c
A
Figure 10.8 - control of a single acting cylinder using OR valve
10.2.5 Control of single acting cylinder using “Not” valve
− Another name for a NOT function is inverse control. In order to hold or lock an operating
conveyor or a similar machine, the cylinder must be locked until a signal for cancelling the
lock is received. Therefore, the signal for cancelling the lock should be operated by a
normally open type control valve.
− However, to cancel the lock, the same signal must also cancel the locks on other devices,
like the indication signal . Figure 10.10 shows how the normally closed type control valve
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.5
Pneumatic Circuits
can be used to cut off the normally open type control valve and achieve the goal of
changing the signal.
m
Figure 10.9 - Control of a single acting cylinder using NOT valve
o
10.3 DOUBLE ACTING CYLINDER CONROL
10.3.1 Direct control of double acting cylinder
.c
− The only difference between a single acting cylinder and a double acting cylinder is that a
double acting cylinder uses a 5/2 directional control valve instead of a 3/2 directional control
valve (Figure 10.10).
ie
h
− Usually, when a double acting cylinder is not operated, outlet ‘B’ and inlet ‘P’ will be
connected. In this circuit, whenever the operation button is pushed manually, the double
acting cylinder will move back and forth once.
e
T
c
e
c
A
Figure 10.10 - Direct control of a double acting cylinder
− In order to control the speed in both directions, flow control valves are connected to the
inlets on both sides of the cylinder. The direction of the flow control valve is opposite to that
of the release of air by the flow control valve of the single acting cylinder.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.6
Pneumatic Circuits
− Compared to the throttle inlet, the flow control valve is tougher and more stable.
Connecting the circuit in this way allows the input of sufficient air pressure and energy to
drive the piston.
Example 3: Pneumatic system is to be designed to operate a door of public transport
vehicles. (Figure 10.11). Assuming that the opening and closing of the doors are controlled
by two button switches ON and OFF. When the button switch ON is pressed, the door will
open. When the button switch OFF is pushed, the doors will close.
m
o
.c
Figure 10.11 - Operation of pneumatic system that controls the door of vehicle
Solution.
ie
h
Solution is given in Figure 10.12, which is self-explanatory
e
T
c
e
c
A
Figure 10.12 - Pneumatic circuit to control the door of vehicle
10.3.2 Indirect control of double acting cylinder using memory valve
− When the 3/2 way valve meant for Forward motion (Figure 10.13 b) is pressed, the 5/2
memory valve switches over through the signal applied to its pilot port 14. The piston travels
out and remains in the forward end position.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.7
Pneumatic Circuits
− Double piloted valve is also called as the Memory valve because now even if this push
button meant Forward is released the final 5/2 control valve remains in the actuated status as
the both the pilot ports of 5/2 valves are exposed to the atmosphere pressure and the piston
remains in the forward end position.
m
o
.c
ie
h
Figure 10.13 - Indirect control of Double acting cylinder using memory valve
− When the 3/2 way valve meant for return motion (Figure 10.13 a) is pressed, the 5/2 way
valve switches back to initial position through the signal applied to its pilot port 12. The
piston then returns to its initial position and remains in the rear end position. Now even if the
Return push button is released the status of the cylinder will not change.
c
e
− The circuit is called a memory circuit because it uses a 5/2 way double pilot memory valve.
5/2 way valve can remember the last signal applied in terms of the position of the spool in the
absence of reset springs, thus memorizing or storing the pneumatic signal. Double piloted 4/2
way valve also can be used as memory valve.
e
T
c
10.4 SUPPLY AIR THROTTLING AND EXHAUST AIR THROTTLING
− It is always necessary to reduce the speed of cylinder from maximum speed based on
A
selected size of final control valve to the nominal speed depending on the application.
− Speed control of Pneumatic Cylinders can be conveniently achieved by regulating the flow
rate supply or exhaust air.
− The volume flow rate of air can be controlled by using flow control valves which can be
either two way flow control valve or one way flow control valve
− There are two types of throttling circuits for double acting cylinders:
i) Supply air throttling
ii) Exhaust air throttling
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.8
Pneumatic Circuits
10.4.1 Supply air throttling
− This method of speed control of double acting cylinders is also called meter –in circuit
(Figure 10.14 a).For supply air throttling, one way flow control valves are installed so that air
entering the cylinder is throttled.
− The exhaust air can escape freely through the check valve of the throttle valve on the outlet
side of the cylinder. There is no air cushion on the exhaust side of the cylinder piston with
this throttling arrangement. As a result, considerable differences in stroking velocity may be
obtained even with very small variations of load on the piston rod.
− Any load in the direction of operating motion will accelerate the piston above the set
velocity. Therefore supply air throttling can be used for single acting and small volume
cylinders.
m
o
.c
e
T
c
e
ie
h
Figure 10.14 - Throttling Circuits
10.4.2 Exhaust air throttling.
c
− This method of speed control of double acting cylinders is also called meter-out (Figure
A
10.14 b). In exhaust air throttling throttle relief valves are installed between the cylinder and
the main valve in such a way that the exhaust air leaving the cylinder is throttled in both
directions of the motion of the cylinder.
− The supply air can pass freely through the corresponding check valves in each case. In this
case, the piston is loaded between two cushions of air while the cylinder is in motion and
hence a smooth motion of the cylinder can be obtained.
− The first cushion effect is due to supply air entering the cylinder through check valve, and
second cushion effect is due to the exhaust air leaving the cylinder through the throttle valve
at a slower rate. Therefore, exhaust air throttling is practically used for the speed control of
double acting cylinders.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.9
Pneumatic Circuits
− Arranging throttle valves in this way contributes substantially to the improvement of feed
behaviour.
10.5 TIME DEPENDENT CONTROLS
− Pneumatic timers are used to create time delay of signals in pilot operated circuits.
Available as normally closed timers and normally open timers. Usually pneumatic timers are
on delay timers.
− Delay of signals is very commonly experienced in applications such as bonding of two
pieces. Normally open pneumatic timers are also used in signal elimination. Normally open
pneumatic timers are used as safety device in two hand blocks
− Time delay valve is a combination of a pneumatically actuated 3/2 direction control valve,
an air reservoir and a throttle relief valve.
− The time delay function is obtained by controlling the air flow rate to or from the reservoir
by using the throttle valve. Adjustment of throttle valve permits fine control of time delay
between minimum and maximum times.
m
− In pneumatic time delay valves, typical time delays in the range 5-30 seconds are possible.
The time delay can be extended with the addition of external reservoir.
o
.c
Pneumatic timer can be classified as
1. On –delay timer
2. Off – delay timer
ie
h
− In on-delay timer, the 3/2 DCV is actuated after a delay with reference to the application of
pilot signal and is rest immediately on the application of the pilot signal. In off delay timer,
the 3/2 DCV is actuated immediately on the application of the pilot signal and is reset only
after a delay with reference to the release of the pilot signal.
c
e
− Pneumatic timers can also be classified according to type of pneumatically actuated 3/2
DCV as:
e
T
1) Time delay valve, NC type
c
2) Time delay valve, NO type.
Time delay valve, NC type. The constructions of an on-delay timer (NC) type in the normal
and actuated are shown in Figure 10.15 It can be seen that 3/2 DCV operates in the on delay
mode permanently. But, in some designs, the valve can be operated in the off-delay mode by
connecting the check valve in reverse direction. For this purpose, the ports of the throttle
check valve should be brought out.
A
Time delay valve, NO type. The construction and function of an on-delay timer (NO) type is
similar to that of an on-delay timer (NC) type except for the type of 3/2 DCV valve. In the
on-delay valve (NO) type, a 3/2 DCV (NO) type is used whereas in the on-delay timer (NC)
type, a 3/2 DCV (NC) type is used.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.10
Pneumatic Circuits
m
Figure 10.15
o
Example 4: A double acting cylinder is used to press together glued components. Upon
operation of a press button, the clamping cylinder slowly advances. Once the fully extended
position is reached, the cylinder is to remain for a time of t = 6 seconds and then immediately
retract to the initial position. A new start cycle is only possible after the cylinder has fully
retracted and after a delay of 5 seconds. During this delay the finished part is manually
removed and replaced with new parts for gluing. The retracting speed should be fast, but
adjustable.
.c
e
T
c
e
ie
h
c
A
Figure 10.16
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.11
Pneumatic Circuits
− If the push button S1 is actuated for a sufficiently long time period (t = 5 second) then the
air reservoir of time delay valve V1 is filled and corresponding 3/2 valve is switched,
following which a signal is applied at input 1 of the dual pressure valve V2.
− If the push button S1 is actuated, the AND condition at the dual pressure valve is met. A
signal is applied at the control port 12 of the control element V4. The valve V4 switches,
pressure is applied to the piston side of the cylinder 1A and the piston rod advances. After as
short advancing distances, the limit switch S2 is released, pressure is reduced in the air
reservoir of the time delay valve V1 via the roller lever valve S2, and the integrated 3/2 way
valve switches back to its initial position. The AND condition at the dual pressure valve is
now no longer met. Actuation of the push button S1 becomes ineffective.
− Upon reaching the advancing position, the piston rod actuates the roller lever S3. The
pressure line to the time delay valve V3 is now released and pressure in the air reservoir is
increased. The rate of pressure increase is adjustable via the integrated flow control valve.
When the switching pressure has been reached, the integrated 3/2 way valve switches and a
signal is applied at the control port 12 of the final control element V4. The valve V4 reverses
and the piston rod retracts. Upon release of the limit switch S3, the time delay valve V3
Switches to its initial position again.
m
o
.c
− The limit switch S2 is actuated, when the piston rod reaches its initial position, the pressure
in the air reservoir of the time delay V1 starts to increase until the switching pressure has
been reached after t = 5 seconds. The integrated 3/2 way valve switches. The initial status of
the system is now reached again and a new cycle can be started. The piston rod speed is set at
the restrictors of the one way flow control valves V5 and V6.
e
T
c
e
ie
h
c
A
Reference Books:
1. Basic Pneumatic Systems, Principle and Maintenance by S R Majumdar, McGrawHill.
2. Hydraulic and Pneumatic Controls: Understanding made Easy, K.Shanmuga
Sundaram, S.Chand & Co Book publishers, New Delhi, 2006 (Reprint 2009)
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 10.12
Automation
EXPERIMENT – 11
AIM – To study about automation in hydraulic and pneumatic systems
11.1 INTRODUCTION
- In today’s fast-moving, highly competitive industrial world, a company must be flexible,
cost -effective and efficient if it wishes to survive. In the process and manufacturing
industries, this has resulted in a great demand for industrial control systems/ automation in
order to stream-line operations in terms of speed, reliability and product output. Automation
plays an increasingly important role in the world economy and in daily experience.
- Automation is the use of control systems and information technologies to reduce the need
for human work in the production of goods and services. In the scope of industrialization,
automation is a step beyond mechanization. Whereas mechanization provided human
operators with machinery to assist them with the muscular requirements of work, automation
greatly decreases the need for human sensory and mental requirements as well.
m
o
11.1.1 What is automation control system?
.c
ie
h
- Automation Control System - system that is able to control a process with minimal human
assistance or without manual and have the ability to initiate, adjust, action show or measures
the variables in the process and stop the process in order to obtain the desired output.
- The main objective of Automation Control System used in the industry are:
1. To increase productivity
c
e
2. To improve quality of the product
T
3. Control production cost
e
11.2 TYPES OF AUTOMATION IN THE INDUSTRY
c
Classification of automation
A
a) Permanent/Fixed Automation
- This control system is designed to perform a specific task
- Functions of control circuit is fixed and permanent.
- It will be complicated if we want to do other task apart from the existing task
b) Programmable /Flexible Automation
- Programmable automation or flexible automation is a complex control
system that can perform several tasks
- Functions of control circuit programmed by the user and can be modified.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.1
- When the task to be performed by machines changed, changes only need to
be done by making modifications to the machine control program.
11.2.1 Comparison between fixed and flexible automation system
FIXED
FLEXIBLE
AUTOMATION
AUTOMATION
Purpose
Specific
Variety
Ease of making changes / upgrade
Difficult
Easy
Maintenance
Hard
Easy
Depends on
Capability
manufacturing and
Very high
design
Speed
Slow
Economy efficiency
Suitable for small
system
Example:
Fixed automation
e
c
A
T
c
e
m
o
Fast
ie
h
.c
Suitable for
all types of systems
Figure 11.1 – Fixed automation
Programmed automation
- There are three types of the control system based on supply
a) Pneumatic control systems
b) Hydraulic control system
c) Electrical control system
a) Pneumatic control system
- Pneumatic control system is a system that uses compressed air to produce power / energy to
perform any task
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.2
- Pneumatic systems found in many industrial systems such as food industry, petrochemical
and industrial involves robotics.
m
o
Figure 11.2 – Programmed automation
.c
- Pneumatic systems requires:
i. Compressed air supply
ii. Control valve
iii. Connecting tube
iv. Transducer
c
e
ie
h
- Pneumatic control system can be controlled manually and automatically.
e
T
c
A
Figure 11.3 - Basic Block Diagram of Pneumatic Control System using manual/PLC
b) Hydraulic control system
- Hydraulic control system is a system that uses fluid to generate power/energy.
- The hydraulic system used in the automobile industry such as power systems, braking
systems, cranes, car jack, satellite and others.
- The fluid used is oil.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.3
- The hydraulic system requires:
a) Hydraulic fluid supply
b) Control Valve
c) Cylinder
- Hydraulic control system can be controlled manually and automatically
m
o
Figure 11.4 - Basic block diagram of an automatic hydraulic control system by Manual /PLC
.c
c) Electrical control system
- A control system that uses an electric current; either direct current (DC) or current shuttle
(AC) as a source of supply.
- Electrical control systems generally requires:
a) Electricity (DC) or (AC)
c
e
ie
h
b) Input elements (switches, sensors, transducer, valves, electronic components, etc.)
c) Output elements (motor, lights, etc.)
d) Extension cable
e
T
c
A
Figure 11.5 - Basic block diagrams of electrical control system using PLC
11.2.2 Comparison between pneumatic control systems, hydraulic control system and
electric control system
i. Pneumatic control system
a) Easy installation
b) Simple design
c) Use compressed air as a supply source to perform task.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.4
ii. Hydraulic control system
a) Complex to assemble
b) Use fluid like oil as a supply source to perform task.
c) Potential leakage will lead to pollution.
iii. Electric control system
a) Simple system
b) Use electricity as a supply source to perform task.
c) Widely use either for home user or in industrial.
11.3 ADVANTAGES AND DISADVANTAGES OF AUTOMATION CONTROL IN
INDUSTRY
The main advantages of automation are:
- Replacing human operators in tasks that involve hard physical work.
m
- Replacing humans in tasks done in dangerous environments (i.e. fire, space, volcanoes,
nuclear facilities, underwater, etc.)
o
- Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc.
.c
- Economy improvement: Automation may improve in economy of enterprises, society or
most of humanity. For example, when an enterprise invests in automation, technology
recovers its investment; or when a state or country increases its income due to automation
like Germany or Japan in the 20th Century.
ie
h
- Reduces operation time and work handling time significantly.
c
e
The main disadvantages of automation are:
- Unemployment rate increases due to machines replacing humans and putting those humans
out of their jobs.
T
- Technical Limitation: Current technology is unable to automate all the desired tasks.
e
- Security Threats/Vulnerability: An automated system may have limited level of intelligence,
hence it is most likely susceptible to commit error.
c
A
- Unpredictable development costs: The research and development cost of automating a
process may exceed the cost saved by the automation itself.
- High initial cost: The automation of a new product or plant requires a huge initial
investment in comparison with the unit cost of the product, although the cost of automation is
spread in many product batches of things
Reference Books:
1. Industrial Hydraulics by John Pippenger and Tyler Hicks, McGraw Hill.
2. Oil Hydraulic Systems, Principle and Maintenance by S R Majumdar, McGraw-Hill.
3. Fluid Power with Applications by Anthony Esposito, Pearson.
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.5
m
o
.c
e
T
c
e
ie
h
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 11.6
Case Study
EXPERIMENT - 12
AIM - To study about the components and functions of various hydraulic and Pneumatic
Systems commonly used in various equipments available in the market.
12.1Methodology:
− The students will perform the case study of any Equipment utilizing Hydraulic and Pneumatic
Systems. Students will identify various components utilized in the equipment and will explain
the functions of each of these components and the working of that pneumatic system.
− To make this more clear two case studies have been presented below.
12.2 Case 1: Hydraulic System
m
o
.c
e
T
c
e
ie
h
c
A
Figure 12.1 - Hydraulic Drive Quick Return Mechanism
12.2.1 Components used and their Functions:
1. Gear Pump: It is used to pump the hydraulic fluid to the Hydraulic Cylinder.
2. Hydraulic Cylinder: There is a piston inside Hydraulic Cylinder which is connected to
the Ram. When hydraulic fluid enters the hydraulic cylinder the piston will move and
which in turn will move the Ram.
3. 4 Way Valve: It controls the direction of high pressure fluid into the cylinder and
controls the direction of motion, either the cutting stroke or return stroke.controls the
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 12.1
Case Study
direction of high pressure fluid into the cylinder and controls the direction of motion,
either the cutting stroke or return stroke.
4. Relief Valve: It is used to limit the system pressure to a specific set level. If this set
level is reached, the pressure relief valve responds and feeds the excess flow from the
system back to the tank.
5. Oil Reservoir: It contains OIl which is pumped in the whole system by the gear pump.
6. Throttle Valve: It is one of the most widely used flow control valve.
12.2.2 Working:
− Quick return in the hydraulic shaper is accomplished by increasing the flow of hydraulic oil
during the return stroke. In the hydraulic shaper the ram is connected to the hydraulic cylinder
which is controlled by means of a 4 way valve.
− The hydraulic fluid is pumped to the hydraulic cylinder through 4 way valve; this valve is
connected to the sump. The 4 way valve controls the direction of high pressure fluid into the
cylinder and controls the direction of motion, either the cutting stroke or return stroke.
m
o
− The flow control valve controls the flow rate of the hydraulic fluid thereby controlling the
speed at which ram moves. Since the power available remains constant throughout, it is
possible to utilize the full capacity of the cutting tool during the cutting stroke. The starting and
stopping of the machine is achieved by through a finger operator lever.
.c
ie
h
− An adjustable trip dog operated lever controls the operation of 4 way valve to control the ram
reversible. The return or idle stroke is faster than the cutting stroke because of the smaller area
in the return side of the cylinder if constant volume pump is used.
12.3 Case 2: Pneumatic System
e
T
c
e
c
A
Figure 12.2 - Pneumatic Auto Feed and Auto Clamp Drilling Machine
12.3.1 Components used and their Functions:
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 12.2
Case Study
1. Air compressor: It is used to convert power using an electric motor, diesel or gasoline
engine, etc. into potential energy stored in pressurized air.
2. Solenoid Valve: They are used to direct the flow of the compressed air. Their tasks are
to shut off, release, dose, distribute or mix fluids.
3. Flow Control Valve: It regulates the flow or pressure of compressed air inside this
pneumatic system.
4. Pneumatic Single Acting Cylinder: It is used for auto feed movement of drilling
machine.
5. Pneumatic Double Acting Cylinder: It is used for clamping the work piece
automatically.
12.3.2 Working:
− The compressed air from the compressor is used as the force medium for this operation. Two
pneumatic cylinders are used. One is used for auto feeding mechanism and another is used for
feeding mechanism.
m
o
− The air from the compressor enters to the four way junction. From four way junctions one
way of air enters to the barrel unit. The other way of air enters the 5/2 solenoid valve. From
solenoid valve air enters to the pneumatic double acting cylinder through flow control valve.
.c
− From 4-way junction, the air also enters to the single acting solenoid valve. This valve is used
ie
h
for automatic work piece clamping operation. The air is entering from single acting solenoid
valve to single acting pneumatic cylinder.
− When the solenoid valve (5/2 and single acting) is in ON condition, the drill head comes
downward and drilling operation occurs. At the same time work piece is clamped by single
acting pneumatic cylinder. After some time, the solenoid valve is OFF; the drilling head and
work piece is automatically released.
e
T
c
e
c
A
Oil Hydraulics and Pneumatics (2171912)
Department of Mechanical Engineering
Darshan Institute of Engineering & Technology, Rajkot
Prepared By: Jainik Makwana
Page 12.3