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Control Valve Selection Requirements

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Control valves abound in every area of industrial process control. Control valves handle all kinds of fluids at temperatures from the cryogenic range to well over 1000°F (538°C). Selection of a control valve body assembly requires particular consideration to provide the best available combination of valve body style, material, and trim construction design for the intended service. Capacity requirements and system operating pressure ranges also must be considered in selecting a control valve to ensure satisfactory operation without undue initial expense.

Information required to select a control valve. Photo Credit : Fisher

The numbers in the orange colored circles in the above control valve diagram corresponds to the serial numbers in the table below where we have given the typical information required to select the right control valve. For example serial numbers 1, 2, 3, 4, 5 represents fluid properties corresponding to serial numbers 1, 2, 3, 4,5 in the table below.

To have a clear understanding of the information required to select a control valve which we have discussed in this article, please read the following:
Because of the tendency to get the selection of control valves wrong, most control valve manufacturers and their representatives have dedicated themselves to helping their clients select the control valve most appropriate for the existing service conditions. To aid in selecting the right control valve, the following information must be provided before the actual sizing and selection process:


S/N   
CONTROL VALVE SELECTION INFORMATION
1 Type of fluid to be controlled What fluid will you be controlling? Water?, natural gas? 
2 Temperature of fluid State the worst scenario temperature of the fluid in degree Fahrenheit or Celsius
3 Viscosity of fluid
4 Specific gravity of fluid
5 Flow capacity of the control valve State the maximum and minimum flow rates.
6 Inlet pressure at valve State maximum and minimum inlet pressures expected to be handled by the control valve
7 Outlet pressure at valve State maximum and minimum outlet pressures expected to be handled by the control valve
8 Pressure drop during normal flowing conditions
9 Pressure drop at shut off
10 Noise level State the maximum permissible noise level if required and the measurement reference point e.g 55 dBA
11 Degrees of superheat or existence of flashing if known
12 Inlet and outlet pipeline size and schedule
13 State whether any special tagging information is required for the control valve
14 Body material of the control valve State the required body material of the control valve - ASTM A216 grade WCC, ASTM A217 grade WC9, ASTM A351 CF8M, etc.)
15 End connections and valve ratings Is it going to be screwed? Class 600 RF flanged? Class 1500 RTJ flanges? etc
16 Valve action desired when instrument air fails Is the valve to fail open, close or retains its last controlled position?
17 Instrument Air Availability State whether the valve require instrument air
18 Valve type number Only when required by manufacturer
19 Valve size
20 Valve body construction Is the valve body going to be angle? double-port? Butterfly? etc.
21 Valve port size State whether the valve port size is going to be full or restricted
22 State the desired valve trim materials required
23 Flow action State whether flow will tend to open valve or close valve
24 Actuator size State the size of actuator required for the control valve.
25 Bonnet Style Is the bonnet style going to be plain, extension,
bellows seal, etc.

26 Valve packing materials State the type of valve packing material - PTFE V-ring, laminated graphite, environmental
sealing systems, etc.

27 Valve accessories State the control valve accessories required – positioner, handwheel etc