Piston actuator, double acting

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

Drawn as

A rectangle (cylinder) on the valve stem with a piston line across the middle and a signal port into each end, with no spring.

Meaning

Cylinder powered in both directions. It stays put on loss of air (fail last), so it is used where the valve must not move on air failure, or with an accumulator. On/off valves (XV) mostly; use esd-valve only if the tag says ESDV/SDV.

Variants

Ports may be drawn as short stubs with pneumatic (//) or hydraulic (L) marks
Often noted "FL" or "fail last"