Operators and fitters pinch back, or pinch in, a valve to reduce flow by a turn or two: slowing a fill, steadying a jumping gauge, or taking load off a pump. It implies small, deliberate adjustment with the valve still passing flow. A valve described as pinched is somewhere between cracked and wide open.
Heard on the job
Pinch back the fill valve on the tank, it's coming up too fast and the level switch is going to trip.
Also heard as
- pinch in
- pinch it down