Needle valves have a slender, tapered point at the end of the valve stem that is lowered through the seat to restrict or block flow. Fluid flowing through the valve turns 90 degrees and passes through an orifice that is the seat for a rod with a cone shaped tip. These small valves are widely used to accurately regulate the flow of liquids and gases at low flow rates. The fine threading of the stem and the large seat area allow for precise resistance to flow.

Needle valves are used to control flow into delicate gauges, which might be damaged by sudden surges of fluid under pressure. 

Needle valves are also used in situations where the flow must be gradually brought to a halt and at other points where precise adjustments of flow are necessary or where a small flow rate is desired. They can be used as both on/off valves and for throttling service. 

Materials

Metal Needle

• Brass
• Bronze
• Stainless steel or other alloys of steel

Elastomeric Seat

• PVC
• CPVC
• PTFE
• Plastics
• Thermoplastics

While this is the most common form, valves are available that have metal - metal, plastic - plastic, or plastic - metal needles and seats. These variations are usually designed with specific applications in mind, especially situations where corrosion, high or low temperatures or extensive wear are possible. In such cases, it is best to consult with the manufacturer to find which type of valve is best for the application at hand.

Applications

Needle valves are used in almost every industry in an incredibly wide range of applications - anywhere control or metering of steam, air, gas, oil, water or other non-viscous liquids is required.

Industries

• Zoological sciences
• Gas and liquid dispensation
• Instrumentation control
• Cooling
• Power generation

Needle valves should be avoided in applications where the media is viscous, or in the dispensation of slurries. The small flow orifice can easily trap thick materials or solids and become blocked.

Standards

BS 7174 P4 - Specification for introducer needles, introducer cannulae, guide wires, dilators, valves, and connectors

MIL-V-24586 - Valves, needle, size 1/4-inch and 1/2-inch

PIP PNDMV09N - Needle valve data sheet and standard terms

Image credits:

HydraForce, Inc. | OMEGA Engineering, Inc.