Control Valve Selection
Control valve selection is depend on below these points :
- 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 (maximum and minimum)
- Pressure drop during normal flowing conditions
- Pressure drop at shutoff
- Maximum permissible noise level, if pertinent, and the measurement reference point
- Degrees of superheat or existence of flashing, if know
- Inlet and outlet pipeline size and schedule
- Special tagging information required
- Body Material (ASTM A216 grade WCC, ASTM A217 grade WC9, ASTM A351 CF8M, etc.)
- End connections and valve rating (screwed, Class 600 RF flanged, Class 1500 RTJ flanges, etc.)
- Action desired on air failure(valve to open, close, or retain last controlled position)
- Instrument air supply available
- Instrument signal (3 to 15 psig, 4 to 20 mA, Hart, etc.)
- Valve type number
- Valve size
- Valve body construction (angle, double-port, butterfly, etc.)
- Valve plug guiding (cage-style, port-guided, etc.)
- 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)
- Actuator size required
- Bonnet style (plain, extension, bellows seal, etc.)
- Packing material (PTFE V-ring, laminated graphite, environmental sealing systems, etc.)
- Accessories required (positioner, handwheel, etc.)