How to Specify Control Valves ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

How to Specify Control Valves

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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.

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