The needle valve is named for the conical rod that acts as a plug over a small diameter hole in relation to the nominal diameter of the valve. The displacement of the rod, if it is of fine thread, is slow and the fact that until a good number of turns is turned the section of passage of the fluid is minimal, it turns this valve into a good flow regulator, for its stability, precision and shutter design that facilitates a good metal seal, with little wear that prevents cavitation at large differential pressures.
It is possible to find designs with the arrangement of the valve inlet and outlet ports angularly, straight (90º) or linear (0º). In hydraulic plants, the needle valves are used as bypass to the butterfly valve or spherical inlet to the turbines. First it is operated with the needle valve, which can work better than the main one at large pressure differences without cavitation, and once the main valve is at balanced pressures its overture is performed avoiding a water hammer of the installation.

How does a needle valve work?

Its function, like the great majority of valves, is to regulate the fluid that passes through a circuit safely and efficiently. The needle valve owes its name to its design, characterized by having a conical rod that acts as a plug over a hole with a diameter much smaller than the nominal diameter of the valve itself.

How does a needle valve work?

Using the steering wheel you can control the distance between the plunger and the seat. Being of fine thread the movement is slow so that many turns are required to achieve a total opening. This gives the valve superior accuracy, stability and sealing. In addition, it gives it great wear resistance as it prevents vacuum aspiration at high differential pressures. These features make needle valves ideal for protecting delicate meters from possible damage caused by sudden changes in pressure. They are generally used for systems that work lighter and less viscous materials with low flow rates.

Uses of the needle valve

Needle valves are generally used in low pressure hydraulic systems, chemical processing and other gas and liquid services. These valves can also be applied to high temperature and oxygen service depending on their materials. Needle valves are usually made of stainless steel, bronze, brass or metal alloys. It is important to choose a needle valve made with the material that best suits the service you need. This will help preserve the life of the valve and keep your systems running smoothly and safely.

What are the functions of a needle valve?

Needle valves play an important role in regulating the amount of a substance released by flow, pressure and direction. These valves also have the ability to cut off the flow completely. They resemble globe valves in function and design, except that needle valves have a tip instead of a disk at the end of the stem.

  1. Function: The needle valve is specifically designed to control the flow of liquid or gas so that it can gradually decrease and finally shut down completely. Needle valves are suitable for starter motor control, since they have a smaller seating area than globe valves. They help protect fragile meters that might otherwise be damaged by the release of large amounts of a pressurized substance.
  2. Threads: The four categories of needle valve stem are thin, thick, moistened and not moistened. The fine threads are thin in appearance and very close together. The control is precise and each turn causes the rod to move in minimum quantities. A thick thread is much wider than the thin one and there is more space between them, to allow a maximum flow and a shutdown with little precision. Wetted stems are defined as threads exposed to the liquid that passes through the system. The non-moistened threads are not exposed to the liquid that passes through the system and remain dry.
  3. Seal: The three types of settlement seals on the needle valves are plastic to metal, metal to plastic and metal to metal. A plastic to metal or metal to plastic seal is ideal for regulating gas flow. Metal-to-metal creates a large sealing surface, which is preferable since gas molecules expand more than liquid ones. A metal-to-metal seal on a needle valve is usually used to regulate the flow of liquid.