Fail indeterminate (FI), letter form
ISA 5.1 / PIP PIC001
Drawn as
The letters "FI" written just below (sometimes beside) a valve body.
Meaning
The fail position is not defined: the valve may drift. Seen on double-acting actuators without a lock-up. Set the valve's fail action to FI.
Variants
- Some legends write "AO/AC" (air to open / air to close) instead. Air-to-open means fail closed
- The fail position is the shelf (no-air) position, not the normal operating position
Tags
FI
Not physical hardware. Read it, then skip it in the 3D model.