ZZYP/ZZYM/ZZYN

Engineer's Selection Guide: Control Valves

Control valves modulate flow in response to a control signal to maintain a process variable. Selection involves sizing for the required Cv, choosing the trim and body style, defining the flow characteristic, and specifying the actuator and positioner. Leakage class per FCI 70-2 should be specified for the duty.

• Size the control valve for a Cv at roughly 60–80% of travel at design flow, leaving rangeability for turndown — oversizing forces the plug into the seat region and causes wear plus poor control.
• Where the fluid flashes or cavitates, move the seat downstream of the plug (flow-to-open) or use characterized multistage trim, and specify the FCI 70-2 leakage class explicitly rather than leaving it open.

Guidance reflects general engineering practice for control valves; confirm against the project specification and applicable standards before procurement.