Fail indeterminate (FI), arrow form
ISA 5.1 (actuator action on failure)
Drawn as
A control valve with one short horizontal bar across the stem between body and actuator.
Meaning
The fail position is not defined: the valve may drift. Seen on double-acting actuators without a lock-up. It is a property of the valve (set its fail action to FI), 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
FI
Not physical hardware. Read it, then skip it in the 3D model.