Needle Valve

A needle valve is a type of valve which having a threaded and a small port , needle-like disc. It is similar  in  design  and operation  to  the  globe  valve.  Instead  of  a  disk, a needle valve has a long tapered point at the end of  the  valve  stem.  A  cross-sectional  view  of  a needle valve is illustrated in figure 6-8.

pressure. Needle valves are also used to control the end of a work cycle, where it is desirable for motion to be brought slowly to a halt, and at other points  where  precise  adjustments  of  flow  are necessary  and  where  a  small  rate  of  flow  is desired.

Although  many  of  the  needle  valves  used  in fluid  power  systems  are  the  manually  operated type (fig. 6-8), modifications of this type of valve are often used as variable restrictors. This valve is constructed without a handwheel and is adjusted to provide a specific rate of flow. This rate of flow will  provide  a  desired  time  of  operation  for  a particular subsystem. Since this type of valve can be adjusted to conform to the requirements of a particular system, it can be used in a variety of systems.  Figure  6-9  illustrates  a  needle  valve  that was  modified  as  a  variable  restrictor.

Application of Needle Valve

Valves is widely used in the process industries like Oil & Gas,Petrochemical, Fertilizers,  Steel, Pharmaceuticals, Beverages, Food and Dairy, Water treatment and OEM applications.

Needle Valve Needle valve is a tool to control the flow of the process media into the instrumentation system.
Thermowell-Thermowell are used to protect the basic sensing element of temperature instruments like Thermometers, sensors, switches etc. from the process media pressure, velocity, viscosity, abrasiveness and corrosion.

Needle valves are mostly used in flow metering applications.Note that the float valve of a carburetor (controlling the fuel level within the carburetor) is not a needle valve, although it is commonly described as one. It uses a bluntly conical needle, but it seats against a square-edged seat rather than a matching cone. The intention here is to obtain a well-defined seat between two narrow mating surfaces, giving firm shutoff of the flow from only a light float pressure.
Since flow rates are low and many turns of the valve stem are required to completely open or close, needle valves are not used for simple shutoff applications.

Since the orifice is small and the force advantage of the fine-threaded stem is high, needle valves are usually easy to shut off completely, with merely "finger tight" pressure. Small, simple needle valves are often used as bleed valves in hot water heating applications.

Unlike a ball valve, or valves with a rising stem, it is not easy to tell from examining the handle position whether the valve is open or closed.

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