Diaphragm actuator (control valve)

ISA 5.1-2009/2022 (final control element actuators) / PIP PIC001

Drawn as

A bow-tie (often with a globe dot) with a stem and a dome-shaped head on top (a half circle sitting on a flat bar).

Meaning

Pneumatic spring-diaphragm actuator: the classic modulating control valve. Its tag (FV/LV/PV/TV) names the loop, and FO/FC beside it gives the fail position. Becomes control-valve.

Variants

The dome may be drawn flat-topped or as a full ellipse
A positioner box on the stem is common
The body may be a butterfly or ball with the same dome for rotary control valves