How to Specify Control Valves

Control valves handle all kinds o fluids at temperatures ranging from the cryogenic range to well over 10000 degree Fahrenheit (538 degree Celsius). Selection of a control valve 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 must also be considered in selecting the right control valve to ensure satisfactory operation without undue initial expense.

Most times the control valve manufacturers and their representatives will help in selecting the most appropriate control valve for a given service conditions. However they require the right set of information to be able to do this as there are several possible correct choices for any given application.

To select a given control valve for any application, follow the steps in the chart below
to supply the required specification information to the manufacturer or their representative:

Specification Chart for Control Valves

Application Information:

Specify the Following:
Inlet pipe size and schedule
Outlet pipe size and schedule
Special tagging information where required
Valve body material
End connections and valve rating (screwed, class 600 RF flanged, class 1500 RTJ flanges  etc)

Process Information:

Specify the Following:
Type of fluid to be controlled
Temperature of fluid
Viscosity of fluid
Specific gravity of fluid
Flow capacity required - Maximum and Minimum
Inlet pressure at valve – Maximum and Minimum
Outlet pressure at valve - Maximum and Minimum
Pressure drop during normal flowing conditions
Maximum permissible noise level and the measurement reference point
Degrees of superheat or existence of flashing if known.
Degrees of superheat or existence of flashing if known.

Valve Trim Information (Where required):

Specify the Following:
Valve type number (optional)
Valve size
Valve body construction (angle, double-port, butterfly etc)
Valve plug guiding (cage style, port-guided)
Valve plug action (push-down-to-close or push-down-to-open)
Port size (full or restricted)
Valve trim materials required
Flow action (flow tends to open valve or flow tends to close valve)
Bonnet style (plain, extension, bellows seals etc.)

Actuator Information:

Specify the Following:
Actuator size
Instrument air supply pressure
Instrument control signal (3 to 15psig, 4 – 20mA, HART etc)
Fail action desired on air failure (valve to open, close, or retain last controlled position)

Valve Accessories Information:

Specify the Following:
Positioner type if required
Limit Switches if required - type , indication etc.
Solenoid if required - type, make , voltage etc.