What is a needle valve and what is the purpose of needle valves

What is a needle valve and what is the purpose of needle valves ?

The needle valve got its name because of its narrow tapered plug and port arrangement. The needle valve is small in size and the control of the fluid flow can be done accurately. Needle valves can be used if the pressure heads or flow rates must be safely reduced and controlled. The needle valves are capable to control the pressure and flow. Needle valves are linear motion valves, these valves are used in instrument systems for throttling of small volumes. Needle valves have metal to metal seats, but because of the small size, they can be used for positive shut off. These valves are capable to control the volume, the delicate gauges flow can be controlled by needle valve which could be damaged by sudden surges of fluid under pressure, needle valves are used where accurate flow control is needed and they are also used where the small rate of flow is required.

How needle valves are constructed?

Needle valve consists of a valve body that has an orifice and a tapered stem and it can be screwed in and out to vary the orifice opening. The flow in both directions can be restricted by the help of needle valves. The preferred direction of flow is indicated by an arrow in the valve body and when the flow is in this direction then the pressure loss across the valve will be less. A needle valve with an internal check valve allows for restricted flow in one direction and free flow in the other direction. Needle valves use the stem to change the size of the orifice and this would give us the ability to compensate for changes in differential pressure in order to maintain a constant flow rate through the valve and a constant actuator speed. It would also allow establishing the desired flow rate without removing the fixed orifice.

How does a needle valve work?

operation of needle valves

The spindle ends in a tampered needle, which would move into the valve seat so that it can restrict or prevent the flow of fluid through it. The in and out motion of the needle to and from the valve seat is controlled by the spindle which is operated by hand wheels. The fluid will turn ninety degrees that go through the valve and it will pass through an orifice, the orifice size can be changed by placing the cone according to the seat. The needle-shaped plunger is on the end of the screw so when the screw is turned the plunger will be retracted, then the flow between the plunger and the seat is possible. The fluid flow will be impeded until the plunger is retracted and the flow rate regulation is possible. Some stems which are properly threaded have slow linear movement so many turns are needed for a full flow section and this makes the needle valve suitable for regulating the flow

 A needle valve can be considered as a small globe valve, it is a form of a globe valve and they are used for low flow. The only difference between the globe and needle valve is instead of a disk at the end of the valve stem it has a long tapered point. The long taper of the valve allows a smaller seating surface area than the globe valve, so the needle valve is more suitable as a throttle valve.

Different types of needle valves

Different types of needle valves include:

Manually Operated Threaded Needle Valve:

 This is the most common type, where the flow is manually controlled by turning a handle that moves the plunger up or down to regulate the fluid flow through the valve.

Motorized Needle Valve:

 These valves are equipped with an electric or pneumatic actuator that automatically adjusts the plunger position. This allows for remote control, precise flow regulation in automated systems, and integration into processes that require timed or continuous adjustment without manual intervention.

Angle Needle Valve:

 Unlike standard needle valves that allow straight-line flow, angle needle valves redirect the flow by 90 degrees. This design is particularly useful for systems where space constraints or piping configurations make a straight-through flow path impractical, while still offering the same precise control over the flow rate.

Needle valve selection

When selecting a needle valve, consider the following key characteristics:

Material:

Brass: 

Suitable for hydraulic systems, drinking water, high-temperature applications, and gas piping. Ideal for neutral and non-corrosive media but not recommended for saltwater, distilled water, acids, or chlorides.

Stainless Steel: 

Offers excellent chemical resistance and durability. Ideal for aggressive and corrosive media, including seawater, although prolonged exposure to saltwater can cause corrosion.

Plastic: 

Used for adjusting pure and corrosive fluids but limited to applications under 60°C due to low temperature and pressure tolerance.

Pressure:

Standard needle valves can handle pressures up to 4,000 to 5,000 psi (275 to 413 bar) at 38°C (100°F). For higher pressures, such as in high-pressure hydraulic systems, select high-performance valves that can manage up to 10,000 psi (689 bar) at 38°C (100°F). For low-pressure applications, vacuum needle designs are available.

Port & Orifice Size:

Needle valves come in various port and orifice sizes. Ports can be male or female with common thread standards including NPT (National Pipe Thread), BSP (British Standard Pipe), or metric (ISO standards). Sizes typically range from 2 to 12 mm or 1/8” to 2”. Choosing the correct size ensures efficient flow and minimizes wear or leakage.

Temperature:

Needle valves can be used in both high- and low-temperature applications. For extreme temperatures, choose the valve housing and sealing materials accordingly. Common sealing materials include PTFE (Teflon) for temperatures ranging from -54°C to 232°C (-65°F to 450°F) and PEEK (Polyether Ether Ketone) for higher temperatures up to 315°C (600°F).

Needle valve symbol

The needle valve symbol typically includes the standard 2-way valve symbol with an arrow or additional marking to indicate that it is a needle valve. In P&ID (Piping and Instrumentation Diagram) schematics, the symbol may be represented as a valve with a diagonal line through the body or an arrow pointing to the flow direction, distinguishing it from other types of valves.

Needle valve vs other valves

When selecting a valve for a specific application, it’s essential to understand the unique features and functionalities of different types. The table below provides a detailed comparison of needle valves, ball valves, and gauge valves. This comparison highlights key differences in operation, function, application, flow control capabilities, and common uses, helping you choose the most suitable valve for your needs.

Needle valve uses

Needle valves are versatile components used across various fluid control applications due to their precise flow rate control. By choosing the appropriate material and size to match temperature and pressure requirements, needle valves can be used for a wide range of clean gases and fluids.

Common Uses of Needle Valves:

Gas Flow Monitoring:

 Needle valves are frequently used to monitor and regulate gas flow, such as propane, by accurately shutting off or adjusting the flow rate. This helps in checking the burn rate for different applications.

Water Systems:

 In dams, reservoirs, power plants, and water distribution systems, needle valves are used to control water pressure and flow rate effectively.

Combustion Control:

 Automated combustion control systems employ needle valves to regulate fuel flow, ensuring precise control over combustion processes.

Flow Metering Devices:

 Needle valves are often used to shut off pressure gauges or adjust flow rates in flow metering devices, providing accurate measurement and control.

Piston Speed Control:

 Needle valves manage the flow of air to cylinders, which helps control the speed of pistons in various mechanical systems.

What are the advantages of the needle valve ?

• The flow control at a low rate is very accurate
• Needle valves are smaller in size
• They can be used for throttling purpose
• Flow rates can be adjusted accurately
• Needle valves are used as bleed valves for hot water heating
• These valves can shut off easily

What are the disadvantages of needle valves ?

• Pressure loss is high in needle valves, because of the high restriction of the fluid flow.
• This valve is used for low flow rates, because of the small passage flow between the seat and needle.
• Damage could happen to the seat and the needle if the fluid has suspended solids.
• We won’t be able to tell if the valve is open or closed by examining the handle position
• Because of the excessive turning force while shutting off the seat of the needle valve could be damaged

What are the applications of needle valves ?

• They can be used on gas bleeder lines
• These alves can be used for sampling lines and for other abrasive services
• Fluid power systems
• These valves are used for flow metering applications
• Needle valves are used in automatic combustion control systems in which accurate flow
  regulation is needed
• Needle valves are used in constant pressure pump governors in order to reduce the effect
  of fluctuations in pump discharge pressure

Relevant standards related to needle valves

This table outlines the key standards that guide the design, performance, and testing of needle valves in different industries and applications.

Leading Needle Valve Manufacturers in the USA

This table provides a quick reference to key manufacturers of needle valves in the USA, highlighting their websites and a brief description of their offerings.

FAQs

What is a needle valve?

 A needle valve is a type of throttling valve designed for precise control of fluid flow rates. It features a tapered plunger that adjusts the flow through a narrow orifice.

What is a needle valve used for? 

Needle valves are used to regulate the flow of fluids in various systems and appliances. They allow for fine adjustments in flow rates due to their small, tapered plunger that controls the opening size of the valve.

Does a needle valve change fluid pressure? 

While needle valves primarily regulate fluid flow, they also influence fluid pressure within a system. By adjusting the valve, you can control both the flow rate and pressure to suit specific requirements.

To know more about other types of control valves and valves check the following link

• Globe valve
• Diaphragm valve
• Control valve installation
• Parts of the control valve
• Control valve and it’s working