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.
Needle valve animation. Video Credit: Unicom Studios
Stainless or other alloys of steel
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.
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.
Gas and liquid dispensation
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.
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
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Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. They are normally used as throttling valves to control flow.
Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves.
Globe valves are linear motion valves with rounded bodies, from which their name is derived. They are widely used in industry to regulate fluid flow in both on/off and throttling service.
Pinch valves include any valve with a flexible elastomer body that can be pinched closed, cutting off flow, using a mechanism or fluid pressure.
Pressure Relief Valves
Pressure relief valves are self-actuated safety valves designed to relieve excess pressure upstream from the line.
Solenoid valves are devices that use a solenoid to control valve activation.
Solids valves are used to control or regulate the flow of powder, granular and other bulk solid materials along a process line, or to and from process units, storage bins, conveyors and product packaging.