What is a Needle Valve? Working Principle & Function
A Needle Valve is a valve that has a small port and a threaded needle-shaped plunger. It allows for fine flow adjustment, however it is usually limited to low flow rates. Manual or motorized needle valves are available. The distance between the plunger and the valve seat is controlled by the handwheel in manually operated needle valves. The plunger is lifted when the handwheel is rotated in one direction, opening the valve and allowing fluid to pass through. Needle valves are often used in flow-metering applications, especially where a constant, calibrated, low flow rate is required for an extended period of time, such as the idle fuel flow in a carburetor.
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What is a Needle Valve?
A needle valve is a type of valve that is used to perfectly control the flow rate of clean gases or fluids. For monitoring the flow rate, the adjustments are gradual and smooth; nevertheless, they can also be utilized as a reliable shut-off valve. They are, however, often employed for low flow rates and have a high-pressure drop from the input to the output. The most common needle valve port diameters range from 1/8” to 2”. The most common application, similar to a propane needle valve, is to control the flow of gas.
Fine shaft movement allows the gearbox to move the piston tube in a sliding motion towards the opening or closing position, according to the needs of the control system.
Needle Valves Working Principle
Needle valves can be used manually or automatically. In manually driven needle valves, the handwheel controls the distance between the plunger and the valve seat. The plunger is lifted when the handwheel is rotated in one direction, opening the valve and allowing fluid to pass through. The plunger slides closer to the seat when the handwheel is spun in the opposite direction, reducing the flow rate or closing the valve.
Automated needle valves have a hydraulic motor or an air actuator that opens and closes the valve automatically. The plunger's position will be adjusted by the motor or actuator in response to timers or external performance data acquired while monitoring the machinery.
Needle valves, both manually operated and automated, provide for fine flow rate control. Because the handwheel is finely threaded, it takes several spins to alter the plunger's position. As a result, a needle valve can assist you in properly regulating the fluid flow rate in your system.
Needle valves use a tapered end that raises and lowers with the turn of a handle to open and close an orifice. The next figure depicts the cross-sectional perspective, design, and components of a needle valve. The plunger, also known as a stem (F), is attached to the handle (A). The plunger travels up or down based on the threads as you spin the handle (C). It can't fully unscrew because of the locking nut (B).
As the plunger descends, the tapered pointed end (I) makes contact with the valve seat, sealing the aperture completely (H). The valve seat is frequently tapered as well. Through the port connection (G) on the input and output, you can connect it to a pipe or hose in a variety of sizes and configurations. The valve housing (E) is attached to the bonnet (D), which can be made of various materials such as brass or stainless steel.
You may precisely situate the plunger's tapered end away from the valve seat using the threads to adjust the flow rate. As a result, you may control the flow rate between maximum and zero by simply adjusting the plunger placement.
Needle Valve Selection
Material, size, pressure, and temperature are the four primary qualities and/or application requirements to consider when choosing a needle valve.
The housing material for the needle valve is chosen based on the application. Brass and stainless steel are the most popular valve housing materials due to their chemical resistance, but other materials are also available for unique uses.
Hydraulic systems, drinking water, high-temperature applications, and gas pipes all benefit from brass needle valves. They are ideal for neutral and non-corrosive media, with drinking water applications being the most typical application. Saltwater (seawater), distilled water, acids, and chlorides, on the other hand, should not be utilized.
Stainless steel needle valves are extremely chemically resistant to practically any medium. The material is extremely tough and resistant to high temperatures and pressures. It can handle corrosive and aggressive media like seawater.
When it comes to choosing the right needle valve, it's crucial to know what your system's pressure needs are. At 100°F (38°C), needle valves can withstand pressures of 4,000 to 5,000 psi (275 to 413 bar). When higher pressures are necessary, such as in high-pressure hydraulic applications, high-performance valves with pressure ratings of up to 10000 psi (689 bar) at 100°F (38°C) are available. When a vacuum needle valve is required to manage low pressure, special designs are available.
Port & Orifice Size
Needle valves come in a variety of port and orifice sizes. Male or female ends can be used for the connection ports. NPT (National American Pipe Thread), BSP (British Standard Pipe), and metric thread standards are commonly employed (ISO standards). The most popular needle valves range in size from 2 to 12 mm (1/8” to 2”) in diameter. Making sure the port and orifice sizes are correct will promote effective flow and system performance with reduced wear and/or leakage.
Needle valves can be used in both high and low temperatures. To ensure that the valve housing and packing/sealing material can survive the requirements, you must specify them adequately, especially for extreme temperatures. PTFE (Teflon) for a temperature range of -65°F to 450°F (-54°C to 232°C) and PEEK (Polyether Ether Ketone) for improved temperature resistance up to 600°F (315 °C) are the two most prevalent sealing materials.
Needle Valve Uses & Applications
Needle valves are often employed to control flow and protect sensitive gauges from damage caused by liquid and gas pressure surges. They're appropriate for systems with modest flow rates and lighter, less viscous materials. Low-pressure hydraulic systems, chemical processing, and other gas and liquid applications all use needle valves.
Because of their materials, these valves can also be used in high-temperature and oxygen applications. Stainless steel, brass, bronze, or metal alloys are commonly used for needle valves. It's vital to choose a needle valve that's composed of the right material for the purpose. This will extend the life of the valve and keep your systems working smoothly and safely.
Because of their ability to precisely control flow rates, needle valves are used in all fluid control applications. They may be used for practically any clean gas or fluid by selecting the right valve material and size for temperature and pressure. One of the most typical uses for needle valves is to monitor gas flow in a system, such as propane. For applications, a propane needle valve can reliably shut it off and/or adjust the flow rate and burn rate.
Needle Valve Construction and Design
Needle valves are similar to shutoff ones. They control the flow rate of a pipeline by starting, stopping, and regulating it. However, needle valves are built differently. Needles, unlike shutoff valves, have a long, tapered needle-like point at the end of the valve stem. The plunger is a term used to describe this device.
The position of the plunger is also controlled by a handwheel or a small lever positioned on the plunger in these valves. The plunger of the valve, which looks like a needle, inserts into the seat. A needle valve can precisely and reliably control the amount of fluid that travels through it due to its unique construction.
Advantages and Disadvantages of a Needle Valve
Advantages of the needle valve include:
- Needle valves are smaller in size.
- The flow control at a low rate is very precise.
- Flow rates can be adjusted accurately.
- They can be used for throttling purpose
- These valves can shut off easily.
- Needle valves are used as bleed valves for hot water heating.
- Disadvantages of needle valves are:
- Because of the substantial limitation of fluid flow in needle valves, pressure loss is high.
- Because of the tiny passage flow between the seat and needle, this valve is utilized for low flow rates.
- If the fluid contains suspended particulates, the seat and needle may be damaged.
- By looking at the handle position, we won't be able to identify if the valve is open or closed.
- The needle valve seat may be damaged as a result of the high turning power used to shut it off.