IEC 60534

Covers — industrial-process control valves: terminology and general considerations, flow-capacity sizing equations (Cv/Kv) for incompressible, compressible, and two-phase flow, inherent flow characteristics, and control-valve testing (issued in numbered parts).

Does NOT cover (exclusions) — the following are governed elsewhere:

• Pressure-relief/safety valves → ISO 4126 / API 520-526.
• On-off isolation valve design → API/MSS valve standards to ASME B16.34.
• Actuator/positioner and control loop tuning → instrumentation standards.

IEC 60534 sizes and characterizes the control valve; safety/relief valves are a separate standard family.

IEC 60534 sets methods and requirements for control valves:

• Sizing Equations — compute Cv/Kv for liquid, gas/vapor, and two-phase flow with choked-flow and geometry corrections.
• Flow Characteristic — inherent characteristics (linear, equal-percentage, quick-opening).
• Testing — flow-capacity and inherent-characteristic test procedures.
• Terminology — standardized definitions (FL, xT, Fk, etc.) used across datasheets.

IEC 60534 is the international standard for industrial-process control valves, harmonized with the ISA 75 series so that both use the same sizing equations. It defines how to compute the valve flow coefficient (Cv/Kv) for liquids, gases, and two-phase flow, with corrections for choked flow, Reynolds number, and attached piping geometry.

It also standardizes control-valve terminology and inherent flow characteristics (linear, equal-percentage, quick-opening). Proper sizing is central: an oversized valve controls poorly near its seat, while an undersized valve cannot pass the required flow. Relief/safety valves are covered separately (ISO 4126 / API 520-526).

Engineering Note: Size control valves to operate in a good controllable range (not near fully open or nearly closed) and check for choked/flashing conditions — a valve sized only on rated Cv can chatter, cavitate, or lose control authority at real operating points.