Control Valves

FLUOR - New Delhi
Control systems engineering
Control Valves
By KK Varma
 Inclusions

Introduction

Flow Characteristics

What is a Control Valve (concept)

Valve sizing coefficient

Classification

Selection criteria

Control Valve symbols

Interface with other depts...

Control Valve Assembly

Applicable codes and standard

Valve Actuator

Major vendors

Valve Positioner

Lastly…
 Exclusions

Preparation of data sheets

Sizing calculations
2
 Introduction (why the need for valves)

Process plants consist of hundreds, or even thousands, of control
loops all networked together to produce a product to be offered
for sale.

Each of these control loop is designed to keep some important
process variable such as pressure, flow, level, temperature etc.
within a required operation range to ensure quality of end
product.

Each of these loops receives and internally creates disturbances
that might detrimentally affect the process.

We gather the information from sensors in field, A controller will
process this info. decide what must be done to get the process
back on track.
3
 Control valve concept
OBJECTIVE:
 Control valve is the final control element in a system.

Control valve is a power-operated device used to
manipulate the fluid (gas, steam, liquid) flow rate in a
process system and keep the regulated process variable
as close as possible to the desired set point.

There are two basic types of control valves :
Linear
Rotary
Each type of valve has its special generic features, which may, in a
given situation, be either an advantage or a disadvantage
4
 Control valve concept
OBJECTIVE:
Linear
Rotary
5
 Control valve classification
Linear Motion
Globe
Globe
Single Seated
Double Seated
Diaphragm
Angle
Pinch or Clamp
3-Way
Split body
Control Valve
Rotary Motion
Butterfly
Swing Through
Eccentric Plug
Lined
Eccentric
Ball
Segmented
Full
V-Notch
6
 Control valves symbols

P&ID symbols of various control valves per ISA S5.1
7
 Control valves symbols ...

P&ID symbols of
various
valves
actuator per ISA
S5.1
8
 Control valves assembly

Control valve assembly typically consists of - the valve
body, the internal trim parts, an actuator to provide the
motive power to operate the valve.
Valve Actuator
Positioner
Valve stem
Valve Body
9
 Actuator operating modes - Linear vlv.
10
 Actuator operating modes - Linear vlv.
11
 Actuator operating modes - Rotary vlv.
12
 Valve positioner

A valve positioner is a
air relay which is used
between the controller
output and the valve
diaphragm. It assures
exact positioning of the
valve
stem
in
accordance
with
controller output
13
 Flow characteristics

The relationship between valve capacity and valve stem travel is
known as the flow characteristics of the valve..
Inherent flow characteristics
14
 Selection criteria

Body size and flow capacity

End connections

Shutoff leakage

Actuator sizing

Valve assembly material

Packing selection

Valve accessories

Special requirement

Noise calculation

Quality requirement
15
 Interface with other depts...

Process
For sizing of valves
For process conditions

Piping
For face to face dimensions
For PDS envelop - (supports if required)
For P&ID markup

Electrical
For electrical actuator power supply (solenoid vlvs.)
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 Applicable codes and standards

ASME B16.34 - valves - flanged, threaded and welding ends

ASME B1.20.1 - Pipe threads

ANSI FCI 70-2 - Control valve seat leakage

ISA 71.01 - Environmental conditions for process measurement & control systems: Temperature and
Humidity

ISA 75.01 - Flow equation for sizing control valves

ISA 75.03 - Face to face dimensions for flanges globe-style control valve bodies

ISA 75.04 - Face to face dimensions for flangeless control valves

ISA 75.17 - Control valves aerodynamic noise prediction

NEMA ICS 6 - Enclosures for Industrial controls and systems

IEC 529 - Specification for degree of protection provided by enclosure

NFPA 70 - National electric code
17
 Major vendors
Valve Assembly
Actuators

Masoneilan Dresser

EIM

Fisher

Bettis

Flowserve (Valtek)

Keystone

Tyco

Automax

Instrumentation Limited

Rotork

Limitork
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 Lastly...
There are lot of other stuff on control valve that should be looked into...
Sizing
calculations (including vendor sizing software’s, INtools)
Datasheets
Generation
Valve
Packing
Valve
Accessories Details
Valve
Noise
Valve
Installations
Hook
up
19
 Over an’ out !
Questions?
20
 Selection criteria contd.


Body size and flow capacity
-
Select valve type
-
Calculate Cv required
-
Select valve/ trim size
End connections
-
End connection type
-
End connection rating
21
 Valve sizing coefficient Cv (basics)

Valve sizing coefficient ‘Cv’ is defined as the number of US
gallons per minute of water that will pass through a given
restriction with a pressure drop of one psi.
Cv =
Q
(P1- P2)/G
This is basic equation for liquid calculations, in
volumetric flow
Where Q - flow rate in US gpm
P1 - upstream pressure in psia
P2 - downstream pressure in psia
G - liquid specific gravity @ flowing temp.
Back
22
 Selection criteria contd.


Shutoff leakage
-
Select seat leakage
-
Class I, II, III, IV, V, VI
Actuator type and size
-
Spring diaphragm, Piston, Cylinder, Double acting cylinder,
Hand wheel, Electric.
-
Check either inlet pressure or maximum shutoff pressure for
actuator sizing
23
 Selection criteria contd.


Valve assembly material
-
Select valve body material
-
trim material (plug, seat, stem or shaft)
-
guide bushing material
-
seat construction as dictated by seat leakage
Packing material and bonnet type
-
Packing - Standard, Teflon (asbestos/ V-rings), Graphoil,
others
-
Bonnet type - Standard (450OF or less), Extended (450OF or
above/ even for cryogenic services)
24
 Selection criteria contd.


Select valve accessories
-
Positioner, Airset, I/P convertor, Solenoid valve, volume
booster, limit switches, travel stop
-
Lo-Db plates or cartridges
Special requirements
-
Cavitation
-
Flashing
-
Two phase flow
25
 Selection criteria contd.


Valve noise
-
Gas and steam noise
-
Liquid noise (cavitation only)
-
Noise treatment (insulation, pipe schedule, noise attenuation
design within valve body, Lo-Db plate, cartridge…)
Quality requirement
-
Non destructive testing
-
Special painting
-
Special packing
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