Fail open (FO), letter form
ISA 5.1 / PIP PIC001
Drawn as
The letters "FO" written just below (sometimes beside) a valve body.
Meaning
On loss of air, power or signal the valve goes fully open. Typical for blowdown valves, cooling-water valves and anti-surge recycle valves. Set the valve's fail action to FO.
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
FO
Not physical hardware. Read it, then skip it in the 3D model.