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FLUOR - New Delhi Control systems engineering
Control Valves
By KK Varma
2
Inclusions
Introduction
What is a Control Valve (concept)
Classification
Control Valve symbols
Control Valve Assembly
Valve Actuator
Valve Positioner
Exclusions
Preparation of data sheets
Sizing calculations
Flow Characteristics
Valve sizing coefficient
Selection criteria
Interface with other depts...
Applicable codes and standard
Major vendors
Lastly…
3
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.
4
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 :
OBJECTIVE: Control valve concept
Linear Rotary
Each type of valve has its special generic features, which may, in a given situation, be either an advantage or a disadvantage
5
OBJECTIVE: Control valve concept
Linear Rotary
6
Control valve classification
Control Valve
Rotary Motion
Linear Motion
Butterfly
Eccentric Plug
Ball
Swing Through
Lined
Eccentric
Segmented
Full
V-Notch
Globe
Diaphragm
Pinch or Clamp
Globe
Angle
3-Way
Single Seated
Double Seated
Split body
7
Control valves symbols
P&ID symbols of various control valves per ISA S5.1
8
Control valves symbols ...
P&ID symbols of various valves actuator per ISA S5.1
9
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
Valve Body
PositionerValve stem
10
Actuator operating modes - Linear vlv.
11
Actuator operating modes - Linear vlv.
12
Actuator operating modes - Rotary vlv.
13
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
14
Flow characteristics
The relationship between valve capacity and valve stem travel is known as the flow characteristics of the valve..
Inherent flow characteristics
15
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
16
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.)
17
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
18
Major vendors
Valve Assembly
Masoneilan Dresser
Fisher
Flowserve (Valtek)
Tyco
Instrumentation Limited
Actuators
EIM
Bettis
Keystone
Automax
Rotork
Limitork
19
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
20
Questions?
Over an’ out !
21
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
22
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
23
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
24
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)
25
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
26
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