A needle valve is a particular kind of valve that has a threaded, needle-shaped plunger with a tiny port. Although it is often limited to low flow rates, it permits precise flow modulation.
A tapered pin is used by an instrument needle valve to progressively open a gap for precise flow control. A spindle can be used to regulate and control the flow.
With a long, tapering seat and a needle-shaped plunger on the end of a screw that precisely fits the seat, a needle valve has a comparatively narrow opening.
Well, in this reading, we’ll explore what a needle valve is, its functions, applications, parts, diagrams, construction, types, and how it works. We’ll also explore its advantages and disadvantages.
Let’s begin!
What is a Needle Valve?
A needle valve is a special kind of valve that has a threaded, needle-shaped plunger with a tiny port. Although it is often limited to low flow rates, it permits precise flow modulation.
A tapered pin is used by an instrument needle valve to progressively open a gap for precise flow control. A spindle can be used to regulate and control the flow.
With a long, tapering seat and a needle-shaped plunger on the end of a screw that precisely fits the seat, a needle valve has a comparatively narrow opening.
Because of its threaded, needle-like plunger, unusually small port, and ability to precisely regulate fluid flow, the needle valve derives its name. The actuator, which might be a little handle or a handwheel, can modify the needle’s position.
Clean gas or fluid flow rates may be precisely controlled using a needle valve. Although they may also be used as a dependable shut-off valve, the adjustments are smooth and progressive for regulating the flow rate.
They have a comparatively considerable pressure drop from the intake to the output, though, and are often only utilized for modest flow rates.
Needle valves typically have ports that are 1/8″ to 2″. The most popular use is to regulate gas flow, much as a propane needle valve.
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Applications
Below are the common uses of needle valves across various industries:
- Used in flow metering applications, especially for maintaining a constant, calibrated, low flow rate.
- Commonly used in carburetor float valves for a well-defined seat between two narrow mating surfaces.
- Provides shut-off for pressure gauges and applicators in anhydrous ammonia applications.
- Not used for simple shutoff applications due to low flow rates and many turns of the valve stem.
- Small orifice and high force advantage make needle valves easy to shut off completely.
- Spindle and seat of needle valves, especially brass, can be damaged by excessive turning force.
- Small, simple needle valves are often used as bleed valves in water-heating applications.
- They are perfect for hydraulic applications because they can accurately control flow rates and resist high pressures.
- In order to maintain the required vacuum conditions, needle valves’ precision control is necessary.
- In applications involving gas, needle valves offer accurate and safe control over gas flow, which is important.
- They are appropriate for water systems because to their corrosion resistance and accurate control over low flow rates.
- For pneumatic systems to operate smoothly, needle valve accuracy and dependability are crucial.
Construction & Working Principle
A tapered pin is used by an instrument needle valve to progressively open a gap for precise flow control. A spindle can be used to regulate and control the flow.
A needle-shaped plunger on the end of a screw precisely fits the needle valve’s long, tapered seat, which has a relatively narrow aperture.
Fluid flow between the plunger and the seat is possible when the screw turns and the plunger is withdrawn, but it is severely hindered until the plunger is fully retracted.
The fine-threaded screw requires several spins to retract the plunger, making it simple to precisely control the flow rate.
The needle valve derives its virtue from the vernier effect of the needle’s length-to-diameter ratio, or the diameter difference between the needle and seat. A very tiny and accurate shift radially (affecting the resulting flow) is made possible by a long trip axially (the control input).
Needle valves can also be employed in vacuum systems, such as when filling gas-filled vacuum tubes, gas lasers, and similar devices, where precise control of gas flow at low pressure is necessary.
Parts of a Needle Valve
The major components of a needle valve include the bonnet, plunger, valve, valve seat, and actuator.
- The bonnet houses the packing and plunger, providing a seal to prevent leakage.
- The plunger controls the size of the orifice and forms a seal when closed.
- The valve seat forms a seal when the valve is closed.
- The actuator, typically a handwheel or handle, adjusts the plunger position, allowing for changes in the orifice size and flow rate.
The function of these basic parts makes needle valves valuable tools in various applications.
Diagram
Types of Needle Valve
There are two types of needle valves, such as angle needle valves and motorized needle valves.
Angle Needle Valve
An angle needle valve is one that rotates the output from the input 90 degrees rather than in line. Although the 90-degree angle can facilitate improved system integration, the same operating principle is applicable as the motorized type.
Motorized Needle Valve
Motorized Needle Valve: These needle valves connect to and rotate the plunger using an electric or pneumatic actuator rather than a handle for human operation.
To precisely manage the flow rate remotely, they can be placed on a timer, operated remotely, or utilized in a closed loop system.
How Does a Needle Valve Work?
A needle valve operates in a straightforward manner. The plunger rises and falls when the actuator is turned. The orifice, or aperture through which fluid may flow, is altered in size by this movement.
The purpose of the needle valve is to regulate fluid flow by changing the orifice size. The flow rate decreases with decreasing orifice size. On the other hand, the flow rate increases with the size of the orifice.
Because of this straightforward fact, needle valves are an extremely useful tool in a wide range of applications.
Every part of the valve, from the gauges to the valve seat and bonnet, is essential to its working. The most crucial part is the valve seat, which stops leaks by creating a seal when the valve is closed.
Both manual and automated operation are possible with needle valves. The handwheel on manually operated needle valves regulates the distance between the plunger and the valve seat.
A hydraulic motor or an air actuator is coupled to an automated needle valve, which opens and closes on its own. Using timers or external performance data collected while the machinery is being monitored, the motor or actuator can change the plunger’s position.
The flow rate may be precisely controlled with both automated and manually operated needle valves. Because of its tiny threading, the handwheel requires many spins to change the plunger’s position.
Consequently, a needle valve may assist you in more effectively controlling the fluid flow rate inside the system.
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Advantages and Disadvantages of a Needle Valve
The benefit of a needle valve is that it is compact in size, and the flow control is at a low rate and very accurate. Also, the flow rates are designed to be accurately adjusted.
The needle valve can be used for throttling purposes, and they can be easily shut off. Finally, needle valves are used as bleed valves for hot water heating.
For limitations, needle valves can easily experience pressure loss because of the high restriction of the fluid flow. They are used for low flow rate because of the small passage flow between the seat and needle.
Needle valves are not ideal for fluids that have suspended solids, as it could easily damage the seat and needle.
Also, you can tell if the valve is open or closed by examining the handle position. This is because of the excessive turning force while shutting off the seat of the needle valve, as they could easily get damaged.
FAQs
What is a needle valve used for?
A needle valve is used to accurately control flow rates of clean gases or liquids. Gradual adjustments of the stem and plunger enable smooth flow control. These valves generally have low flow rates and a relatively significant pressure drop from the inlet to the outlet.
Where is the needle valve located?
Needle valves, also called adjusting controls or fine-adjusting valves, are usually found downstream of the safety shut-off valves (SSOVs) on the burner gas train, though they can also be found on the burner air train. This type of valve is used to dial-in the flow of gas or air and is installed near the burner.
What is a needle valve particularly suitable for?
They’re ideal for systems using lighter and less viscous materials with low flow rates. Needle valves are usually 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 based on their materials.
What is the difference between a needle valve and a globe valve?
Globe valves are for high-pressure apps with accurate flow control and shut-off capabilities. Needle valves regulate low to moderate flow rates and provide precise control.
What is the major difference between a needle valve and a flow control valve?
Although the basic function is flow restriction, the fundamental difference between the two is the needle valve controls flow in both directions (bi-directional), and the flow control valve controls flow in only one direction (allowing free flow in the opposite direction).