a needle valve is mostly the device which helps to umpire the upsurge of fuel in to the device. This is really important,given an extreme volume of fuel can throttle the carburettor, as well as close down  the engine.

It is this ability to control flow with such exactness that makes the needle flow ideal for situations in which the desired flow must be maintained with little to no variance. One common use of both stainless steel and brass needle valves is with utility meters where there is a need to measure precisely the amount of power, water or natural gas that a customer has consumed during a given billing period. At the plant level, valves of this type are often used to regulate the flow into the system used to deliver the product to various points of destination. By controlling the needle valve rate, stress on the delivery system is kept to a minimum, which in turn helps to enhance the safety of personnel who work at various points along that system.

For engines in which carburettors are commonly included, a needle valve is often the device that helps to regulate the flow of fuel into the device. This is very important, since an excessive amount of fuel can choke the carburettor, and shut down the engine. At the same time, a lack of sufficient fuel flowing into the carburettor will result in additional wear and stress on the engine over time, a factor that may lead to costly repairs. An alternative to using a needle valve is the inclusion of what is known as a float valve. In some situations, this type of valve is also identified as a needle-type valve, although the design is different.

A needle valve is also sometimes used in equipment that controls the temperature of water within a specific system. For example, some residential water heaters utilize this type of valve as a type of bleed valve that makes it possible to relieve pressure on the water flowing through the device. As with other applications, the valve makes it possible to control the flow of water through the heater, a factor that can also aid in minimizing the amount of energy needed to maintain an equitable supply of hot water.