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Needle Valve

Technology and inventions have made our life a lot easier. Be it the food we eat, or the clothes we wear, or the soap we bath, or the car we drive. Similarly, valves are one such technological invention that plays a significant role in many industries which affect our day-to-day life.

Talking of valves, there are different types, and each type has unique usage. One such usage of a valve is precise flow control of the fluid, which is achieved by a unique valve known as a Needle Valve.

In this article, we will be discussing needle valves which are used explicitly for very accurate flow controls. So, let’s begin.

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What Is a Needle Valve?

Needle valves are regulating valves that enable engineers to precisely control and regulate the flow of clean gases or fluid. They are also commonly known as Plunger valves.

Needle valves and globe valves are very similar in construction, except that need valves have a plunger with a pointed needle-shaped valve instead of a disk. They also have a small port and finely threaded plunger.

The arrangement permits a gradual increase or decrease in the size of the opening, which allows precise regulation of flow.

How Does The Needle Valve Work?

how does need valve works

Before understanding the working, let’s have a look at the construction of the needle valve.

Needle valves are generally small in size with small inlet and outlet ports. These valves consist of a threaded plunger with a tapered point end. The pointed end sits on an orifice-like opening in the valve body. The plunger is very finely threaded and connected to a hand wheel at the top for manual operation.

With the help of the handwheel, you can very precisely set the needle-like tapered valve end away from the valve seat to control the flow rate accurately. Therefore, by rotating the plunger clockwise or anticlockwise, you will be able to control the flow rate between maximum and zero.

Types Of Needle Valve

Needle valves are of two types based on the mode of operation, i.e.,

  1. Manual needle valve
  2. Automatic needle valve

A manually operated threaded needle valve is the most common type of needle valve. These are generally found in two variants motorized and angle.

Automatic Needle Valve: These needle valves use an electric or pneumatic actuator to connect to and turn the plunger instead of a manual handle. These valves can be remotely controlled, used in a closed-loop system, and put on a timer to accurately control the flow rate remotely.

Angle Needle Valve: These needle valves turn the direction of flow of fluid from the inlet by certain degrees instead of flowing straight out. The same concept applies as that of an angle globe valve, but the 90-degree angle allows better system integration.

Advantages and Disadvantages of Needle Valve

Needle valves have the following advantages:

  • The flow control of fluids or gases at a low rate is very precise and accurate.
  • Flow rates can be adjusted accurately.
  • The Needle valves are specially used in applications where accurate throttling is required.
  • These valves can shut off easily.
  • Needle valves are used as bleed valves for hot water heating
  • Needle valves are smaller in size

The disadvantages of Needle valves along with the reasons.

  • Pressure loss is high due to high fluid flow restriction in needle valves
  • Excessive turning force damages the seat while shutting off the valve.
  • This valve can be used only for low flow rates because of the small passage flow between the seat and needle.
  • It is difficult to make out whether the valve is open or close by examining the handle position.
  • The presence of suspended solids may damage the seat of the needle valves.

Needle Valve Selecion Guide

The selection of needle valves depends upon four main characteristics and application requirements. They are as follows:

  1. Material of Construction
  2. Fluid Pressure
  3. Port or Orifice Size
  4. Fluid Temperature.

Let us understand the significance of each one by one.

Material Of Construction

The housing material of the needle valve is decided according to the application it will be used. Brass and stainless steel housing materials are commonly used due to their sustainability over a wide range of fluids(i.e., corrosive gasses, chemicals, and other liquids). However, there are different materials also available for specific applications.

Fluid Pressure

Usually, robust needle valves can handle pressure up to 5000 psi at 100oF (38oC). When the needle valve is required for higher pressures, like in the case of hydraulic applications, high-performance valves are also available in the market to serve the purpose. Similarly, specially designed valves are used to handle lower pressure or vacuum conditions.

Port or Orifice Size

A wide range of port and orifice sizes are available for various applications of needle valves. The most common size is 2mm to 12mm (1/8" to 2"). Ensuring the correct orifice size ensures sufficient operation and less leakage or chances of wear of valve.

Fluid Temperature

Needle valves are suitable for both high and low-temperature operations. Still, in case of extreme temperatures, one needs to be specific in the selection of the housing material and the packing/sealing material appropriately. This is to ensure the needle valve can meet the extreme temperature requirements.

Where are Needle Valve Used

Needle valves are used in a variety of applications that require flow or pressure regulations. Needle valves are found in all fluid control applications due to their ability to control flow rates precisely. By selecting the right valve material and size for temperature and pressure, they can be used for almost any clean gas or fluid.

  1. Needle valves are vastly used as a safety valve before all pressure gauges that show the pressure of the operating fluid so that a sudden surge of pressure does not damage the gauge.
  2. One of the most commonly used locations for needle valves is to monitor gas flow, like propane, in a system. A propane needle valve can accurately shut the propane off and control the flow rate, thus effectively control the burn rate.
  3. In water treatment plants, dams, reservoirs, power plants, and industry, needle valves are, e.g., used for various purposes. They are as follows;
    • Flow Control
    • Pressure Regulation
    • Pump Start
    • Turbine BY-Pass
    • Discharge
    • Reservoir inlets
    • Air Regulation

        4. These valves are widely used in flow meters applications to gauge the amount of process fluid.
        5. Needle valves are also used in an automatic combustion control system where an accurate fuel flow is required.

How To Install A Needle Valve?

1. Set the gasket between the flanges.

2. Insert washers and bolts from the pipe side, insert washers and nuts from the valve side, and then temporarily, hands tighten them.

3. The parallelism and axial misalignment of the flange surface should be as per the values in the maker’s manual to prevent damage to the valve.

4. Tighten the bolts and nuts gradually with a torque wrench to the specified torque level in a diagonal manner.

Operating Procedure Of Needle Valve

  • Open and close the valve by rotating the handwheel slowly.
    Right turn (Clockwise direction) → Flow quantity is decreased.
    Left turn (Counterclockwise direction) → Flow quantity is increased.
  • Turn the handle to set the direction needle to the mark of the expected open degree.
  • Set the direction needle to indicate the shut position of the valve.

Maintenance Of Needle Valve

Generally, needle valves are maintenance-free in nature. They require proper supervision during their operations. In case of any leakage or improper operations, it becomes necessary to carry out maintenance. So, let us discuss the dismantling and assembly procedures.

Dismantling Procedure

  1. Drain fluid completely from the pipeline.
  2. Turn the handle of the valve counterclockwise to full open. (Too much force may damage the valve.)
  3. Remove the bonnet from the body.
  4. In the case of 15mm and 20mm, Cap can be removed.
  5. Remove the spindle and check the condition of the orifice and o-rings.
  6. Check for the existence of scratches, cracks, deformation, and discoloring
  7. Check for signs of leakage when the valve is opened fully at right or left.

Assembly Procedure

Before commencing the assembly, clean all the parts thoroughly. It is recommended to replace the o-rings with new ones before every assembly.

  1. Before fixing the bonnet, turn the handle clockwise to a fully open position.
  2. Fit the line mark of the body and bonnet.
  3. Tighten the bonnet as required.
  4. After assembly, turn the handle clockwise to complete shut and make sure that the direction needle is set to the mark of zero.
  5. Open the flowing medium check for leakage. If no leakage is detected, restore operations by throttling the needle valve.

Summary

Needle valves are the first choice in cases where precision and accuracy of flow are a priority. Its versatile usability range makes it popular in all types of industries.

Finally, we have reached the end of this article. I am sure that you got a good insight into the technical and engineering aspect of needle valves. This knowledge will guide you to make an appropriate selection of Needle valves as per your requirement. So are you ready for purchase!

Drop a message for any queries related to the Needle valve. We will be happy to help you make the perfect selection. Also, please do not forget to share your valuable comments and suggestions in the section below.