ISA 75

Covers — control valve sizing equations (ANSI/ISA-75.01.01), terminology (75.05), inherent flow characteristics, and flow/capacity testing for industrial-process control valves; the North American series harmonized with IEC 60534.

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

• Pressure-relief/safety valves → API 520-526 / ISO 4126.
• On-off valve pressure ratings → ASME B16.34 and the API/MSS valve standards.
• Actuator sizing and control-loop tuning → other ISA instrumentation standards.

ISA 75 and IEC 60534 are harmonized equivalents — the datasheet may cite either.

The ISA 75 series sets methods and requirements for control valves:

• Sizing — Cv sizing equations for liquid, gas/vapor, and two-phase flow (harmonized with IEC 60534).
• Terminology — standardized definitions and symbols (75.05).
• Characteristics — inherent flow characteristics and rangeability.
• Testing — flow-capacity and characteristic test methods.

The ISA 75 series is the North American control valve standard set — sizing equations (ANSI/ISA-75.01.01), terminology (75.05), characteristics, and testing — harmonized with IEC 60534 so both use the same underlying equations. On any given project a control valve is typically sized and specified to one or the other, with identical results.

The practical value is consistency: using the same defined terms (FL, xT), the same inherent characteristic, and the same choked-flow treatment between the process sizing calculation and the vendor's selection avoids mismatched valve performance. Relief/safety valves fall under API 520-526 / ISO 4126.

Engineering Note: Because ISA 75 and IEC 60534 are harmonized, focus on applying the parameters consistently (not on which standard is cited) — a valve "sized to ISA 75.01" and one "sized to IEC 60534" should give the same Cv for the same conditions.