Needle valves

A needle valve is used for precise control of the flow rate of pure gases or liquids through gradual adjustment of the stem and piston. The valves are typically used at low flow rates, and they result in a relatively significant pressure drop from inlet to outlet. Sizes typically range from 1/8″ to 2″ (2 to 12 mm). The most common use of a needle valve is to control gas, such as propane in a tank.

The piston or stem of a needle valve has a tapered end that is raised and lowered by turning a handle to open or close an orifice. When the handle is turned, the stem moves up or down through the threads. The lock nut prevents the stem from being completely unscrewed. When the stem moves down, the pointed (tapered) end contacts the valve seat to completely seal the orifice. The valve seat is often also tapered. This allows for precise control of the flow rate. Needle valves can be threaded, flanged, or welded.

Advantages of needle valves include the ability to fine-tune flow. Disadvantages include pressure loss, needle and seat damage from contact with larger particles, and the inability to see the position.