Needle valve

An instrument needle valve uses a tapered pin to gradually open a space for fine control of flow.

Since it takes many turns of the fine-threaded screw to retract the plunger, precise regulation of the flow rate is easily possible.

A long travel axially (the control input) makes for a very small and precise change radially (affecting the resultant flow).

Since the orifice is small and the force advantage of the fine-threaded stem is high, needle valves are usually easy to shut off completely, with merely "finger-tight" pressure.

The spindle and/or seat of a needle valve, especially one made from brass, are easily damaged by excessive turning force when shutting off the flow.

Giffard steam water injector (B-needle valve).
A needle valve.
Electrically automated needle valve fluid on a fluid processing system.