A slender conical point on the end of a fine-threaded stem closes into a small orifice, so many turns produce a small change in opening. That makes needle valves the standard choice for instrument root valves, gauge isolation, sample points, and bleeds on manifolds. The small passage clogs in dirty service, and overtightening the needle will gall or deform the seat.
Gauge is bouncing all over, pinch the needle valve back until it settles down.
Snug on the handle is shut on a needle valve. Put a wrench on it and you ruin the tip and the seat.
Also heard as
- needle
Related terms
Bleeder
A small vent or drain valve used to release pressure or fluid, especially between two block valves.
Pinch back
To close a valve partway to cut flow or pressure, without shutting it.
Globe valve
A linear-motion valve that throttles well because its disc moves straight onto a seat across an S-shaped flow path.
Seat
The surface inside a valve that the closure member presses against to stop flow.