Piston actuator, single acting (spring return)

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

Drawn as

A valve with a rectangle (the cylinder) on its stem; inside it a horizontal line (the piston) with a zig-zag spring above it.

Meaning

Air or hydraulic cylinder with spring return. On/off shutdown valves (ESDV, SDV, XV) use it so the spring drives the valve safe on loss of air. With an ESDV/SDV/XV tag it becomes esd-valve; with BDV it becomes blowdown-valve.

Variants

Spring and piston are often omitted: a plain rectangle on the stem
Scotch-yoke quarter-turn actuators are drawn the same on a ball valve
ISA 5.1-2009 draws the piston actuator as a rectangle with the stem through it