Needle valve

A needle valve uses multi-turn stem travel to move a slender, shaped tip gradually toward or away from a seat. The fine movement changes the flow area in small increments, enabling more precise throttling than rapid on-off valve types. Because the available flow area changes with the position of the stem tip relative to the seat, flow coefficient and pressure loss should be checked against the required duty. Unlike a diaphragm valve, sealing and regulation depend on the stem tip and seat. Tip geometry, flow coefficient, packing, flow direction, and required shutoff performance must be selected for the duty.