Like all valves, a Needle Valve is used to control the flow of a fluid (the fluid could be liquid or, it might be gaseous). A Needle Valve is so named because it opens and closes by axial movement of a relatively long tapered pin that resembles a needle in shape. One end of the “needle” is in the seat when the valve is fully closed and the other is threaded so that it can be rotated from the outside to provide the movement and slowly withdraw the “point” out of the seat to allow fluid to flow. Because of the plunger’s long length and small diameter, a vernier like effect is achieved which results in long axial movement producing very small but precise radial movement at the seat giving good control over the fluid flow rate.
Needle valves are normally only used on applications with a relatively slow flow rate. With the relatively slow flow rate through a Needle Valve, this type of valve will require many rotations of the valve stem to fully open or close the valve; hence, needle valves are not used as basic flow/no flow control valves.
Unlike most other valve types, visual examination of the valve handle’s position does not clearly inform an operator if the valve is open or closed. However, a Needle Valve is relatively easy to shut off completely and only requires normal “finger control” to stop the fluid flow. A side effect of this is that the interface between needle and seat is prone to damage if the handle is screwed too tightly when closing a Needle Valve.
Needle valves are popular for the bleed valves in water heating applications. A Needle Valve can also be useful for flow metering control where a constantly accurate slow flow rate must be maintained for some time.
Again, like any other valve, a Needle Valve will be inserted at strategic places within a pipe or tube carrying fluid. Since the valve may have to be removed from time to time, it is rare to weld or braze it into the line pipe. Therefore, a Needle Valve will usually have threads on both its input and outlet orifices.
The purchaser will usually specify the style of end fixings. The initial choice is between male and female (you can even have male on one end and female on the other). The thread may include a tapered flare. Some needle valves are designed to be joined to the mating pipe with compression fittings while others are standard male into female threaded connections with some sort of sealing washer. Although the fittings are theoretically self sealing, most fitters will apply thin ptfe thread tape to the male threads to further seal off the assembly. For more information, visit the website.
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