Top-mounted or side-mounted handjacks let an operator drive the valve against the actuator spring when air is lost, or limit its travel as a mechanical stop. It is also a verb: to handjack a valve open. The handjack must be backed off to neutral before the valve goes back on auto, or the actuator cannot stroke the full range.
Air's down on the reflux valve, handjack it to about 40 percent until instrument air comes back.
The classic post-turnaround bug is a control valve that won't open past 60 percent because someone left the handjack wound in.
Also heard as
- handwheel override
- manual override
Related terms
Actuator
The powered device that opens, closes or positions a valve using air, hydraulic oil or an electric motor.
Spring-return
Describes a single-acting actuator that uses air to move one way and a spring to move back and fail safe.
Stroke
To run an automated valve through its full travel to prove it moves, seats and reports position correctly.