Needle valves are used to accurately control flow rate. They are also suitable as reliable shut off valves. Common sizes are from 1/8” up to 2”. Adjustments are gradual and smooth. A disadvantage of needle valves is the relatively large pressure drop.
Function of needle valves
Needle valves have a long-threaded plunger with a needle-shaped tapered pointed end. This tapered end can be positioned within a tapered valve seat. By rotating the threaded plunger, the tapered end can be precisely distanced from the tapered valve seat. Thereby the valve opening and consequently the flow rate can be accurately controlled between maximum and zero. In most cases, the inlet and outlet port are co-axial to each other. However, different valve configurations are available. They are generally operated manually or motorized allowing automation.
Selection Criteria
Pressure: The working pressure is an important factor in selecting the right needle valve. Robust ones can handle pressures of up to 4000-5000 psi (275-413 bar) at 100°F (38°C). When still higher pressures are required, high performance valves are available that can handle up to 10000 psi (689 bar) pressure at 100°F (38°C).
Size: Needle valves are available in a wide range of sizes and end connections. Male/female connections with inch/metric threads can be used. The most commonly available valves have size from 2 to 12 mm or 1/8” to 2”. Using the right valve size facilitates efficient flow and system operation with less chances of wear and leakage.
Temperature: Needle valves can be operated at high or low temperatures. For extreme temperatures the packing/sealing used is particularly relevant. Two most commonly used packing materials are PTFE (Teflon) for a temperature range of -65°F to 450°F (-54° C to 232°C) and PEEK (Polyether Ether Ketone) for increased temperature resistance up to 600°F (315 °C).
Materials: A number of different materials are used in the valve’s construction. The commonly used materials include brass, 304 or 316 stainless steel, carbon steel and Alloy 400 (Nickel based alloy).
Stainless steel is widely used for its corrosion resistance, chemical stability and high temperature resistance. Brass ones are used in hydraulic systems, high temperature applications and gas piping. Alloy 400 is used for its high strength, corrosion resistance and used mainly in marine and chemical processing applications.
Need a needle valve? Visit Tameson’s online store for a wide range of sizes, material selections, and pressure ranges giving you a valve you can count on at the lowest price for any application. If you need further information or assistance, please visit Tameson’s technical information center.
