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We were discussing hydraulic flow control valvespressure compensated flow control valves and non-pressure compensated flow control valves in our previous post, where we have seen the basic concept and application concept of flow control valves in hydraulic units. We have also seen the working principles of gate valve in our previous posts.

Today we will concentrate here the working principle of “Needle valves” with the help of this post.  Needle valves are basically used in fluid pipelines for controlling the flow of fluid. If we look the design and operating mechanism of needle valves, we will come to understand that needle valves are quite similar in design and operating mechanism with globe valves.

There will not be a disc assembled with valve stem as in globe valve, but there will be one tapered and slender point at the end of valve stem in such type of valves and it will control or restrict the fluid flow.

There will be one handle wheel, as shown in figure, assembled with stem of valve and this handle wheel is used to open and close the needle valve. When handle wheel will be rotated, it will move the tapered and slender point of the valve in upward or downward direction.
Needle Valve
We can see here the figure of a needle valve, where we will come to know that there will be two section of needle valve. Bottom section will be connected with the inlet line and outlet line with the help of flanges and upper section of needle valve will consist with one long valve steam and highly précised and engineered tapered and slender point at the end of long stem. Precise threading of valve stem and larger area of valve seat permits the precise control over the flow of fluid flowing through needle valve.

Working mechanism of a needle valve

Needle valve will provide the precise control over the fluid flow. When handle wheel will be rotated in clockwise direction, steam and its tapered and slender point will move in downward direction and will be tightly fixed into a vale seat provided over the inlet and hence there will not be any leakage of fluid through the valve once valve is closed completely.

When handle wheel will be rotated in anti-clockwise direction, steam and its tapered and slender point will move in upward direction and valve will be opened from closed position and will permit the flow of fluid through the valve. Fluid flowing via needle valve will turn at 90 degree angle and will pass through the valve seat at which slender or tapered point of valve stem will be seated during closed position of valve.

Applications of needle valve

  1. Needle valves are basically used for controlling the fluid flow into the delicate gauges of the system, which might be damaged if high pressure fluid will be delivered suddenly.
  2. Needle valves could also be used in various industrial equipment where motion of work must stop slowly at the end of operation.
  3. Needle valves are usually used for controlling and adjusting the fluid flow precisely. Needle valves are much in demand where lower flow rate will be required.
  4. Needle valves could be used under throttling condition, complete open condition or in complete closed position.

Variation with other flow control valves

Needle valves are slightly different with other flow control valve because needle valves are bi-directional valves and could be used for controlling the fluid flow in both direction, while other flow control valve will control or restrict the fluid flow in one direction only as there will be one check valve for providing the free flow of fluid in reverse direction.

We will discuss Color codes for hydraulic pipelines in our next post.

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Image courtesy: Google

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