Fail open (FO), arrow form
ISA 5.1 (actuator action on failure)
Drawn as
A control valve with an upward arrowhead drawn on the stem between body and actuator.
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. It is a property of the valve (set its fail action to FO), not a separate item.
Variants
- The letter form writes the letters below the body instead
- The bar forms for FL/FI come from secondary sources describing ISA 5.1 and are less widely used than the letters; check the legend
- On 3-way valves, arrows on the ports show the failed flow path
Tags
FO
Not physical hardware. Read it, then skip it in the 3D model.