Small sizes of globe valves are known as needle valves, equipped with a finely tapered plug. A needle valve is a form of valve with a tiny port and a threaded plunger in the shape of a needle.
Although usually only capable of comparatively low flow rates, it enables accurate flow regulation.
Applications of Needle Valves :
A needle valve has a comparatively tiny orifice at the end of a screw that suits the seat precisely, with a lengthy, tapered seat and a needle-shaped plunger.
As the screw is turned and the plunger retracted, it is feasible to flow between the seat and the plunger ; however, the fluid flow is considerably impeded until the plunger is fully retracted.
Since retracting the plunger takes many turns of the fine-threaded screw, it is possible to accurately regulate the flow rate.
The virtue of the needle valve is due to the vernier impact of the proportion between the length and diameter of the needle, or the diameter difference between the needle and the seat.
Needle valves can also be used in vacuum systems at low pressure when accurate control of gas flow is needed, such as filling gas-filled vacuum tubes, gas lasers and comparable devices.
Since the orifice is tiny and the force benefit of the fine-threaded stem is high, it is generally simple to shut down the needle valves entirely with a mere “finger-tight” pressure. A needle valve’s spindle and/or seat, particularly one made of brass, is readily damaged when shutting off the flow by excessive turning force.
Uses:
- Usually, needle valves are used in flow metering applications, particularly if a steady, calibrated, low flow rate has to be maintained for some moment
- Commonly used to provide shut off for the pressure gauge or on applicators to shut off the supply of NH3 to the knives in Anhydrous Ammonia (NH3) applications.
