[140] Needle restrictor
Throttle and orifice valves
are used to achieve a certain pressure drop. This is done by
creating a specific flow resistance. The needle flow control
valve shown generates considerable friction due to its long
narrowing. This means that the action of the flow control valve
is difficult to adjust due to the fact that a small adjustment
produces a large change in cross-section.
One advantage is the simple and inexpensive design. Needle flow control valves can be used if the above- mentioned negative properties can be ignored for the purposes of a given control task.