Valve needles are manual valves used where slowing down of continuous flow is needed for regulation. Needle valves similar to globe valves which are designed with the biggest difference are sharp needles such as disks.
Needle valves are designed to provide highly accurate flow control in small diameter piping systems. They got their names from sharp cone discs and matching chairs.
The function of the needle valve is to accurately control the flow rate of the gas or liquid. Gradual adjustments and smooth movements to control flow rates, however, they can also be used as reliable closing valves. But generally it is only used for low flow rates and has a relatively large pressure drop from the inlet to the outlet.
And the common port sizes for needle valves range from 1/8 "to 2". The most common application is to control the flow of gas, as well as valve propane needles.
How needle valves work
The needle valve opens and closes the hole with a tapered tip that rises and falls with the handle round. Figure 2 describes the appearance, design, and cross-section of the needle valve. The handle (A) is connected to the pusher, also called rod (F). When you rotate the handle, the plunger moves up or down based on thread (C). The locking nut (B) prevents it from being completely detached. When the plunger moves down, the tapered tip (I) touches the valve seat to completely close the hole (H). Often, the valve seat is also tapered.
There are various options and sizes available to connect it to a pipe or hose through a connection port (G) at the input and output. The hood (D) is connected to the valve housing (E), which can be made from different materials such as brass or stainless steel.
Different types of needle valves
Angle needle valve
A manually operated threaded needle valve (described above) is the most common type of needle valve. However, two additional variants are: motorized and angle.
Angle Needle Valve: These needle valves turn the output from the inlet by 90 degrees instead of in-line. The same operation concept applies, but the 90-degree angle can allow for better system integration.
Motorized Needle Valve:
These needle valves don’t have a handle for manual operation, but instead use an electric or pneumatic actuator to connect to and turn the plunger. These can be remotely controlled, used in a closed loop system, and/or put on a timer to accurately control the flow rate remotely.
Needle valve selection
When choosing a needle valve, four main characteristics and / or application requirements need to be taken into account: material, pressure, size and temperature.
The most common valve cover materials are brass and stainless steel because of their chemical resistance range, however, there are also other materials available for special applications.
Brass needle valves are suitable for hydraulic systems, drinking water, high temperature applications, and gas pipes. They are suitable for neutral and non-corrosive media, with the most common implementation being for drinking water applications. However, they may not be used for salt water (sea water), distilled water, acid or chloride.
Stainless steel needle valves have excellent overall chemical resistance for almost all media. The material is very durable and can withstand high temperatures and pressures. It is suitable for aggressive and corrosive media such as sea water.
Understanding the application requirements for pressure in your system is important for selecting the correct needle valve. Robust needle valves can handle pressure of up to 4,000 to 5,000 psi (275 up to 413 bar) at 100°F (38°C). When higher pressures are required, like for high pressure hydraulic applications, high performance valves are available that can handle up to 10000 psi (689 bar) pressure at 100°F (38°C).
Port & orifice size
Needle valves are available in a wide range port and orifice sizes. The connection ports can also be male or female ends. Common thread standards used are NPT (National American Pipe Thread), BSP (British Standard Pipe), or metric (ISO standards). The most commonly used needle valves range from 2 to 12 mm or 1/8” to 2”. Ensuring the correct port size and orifice size will ensure efficient flow and system operation with less chances of wear and/or leakage.
Needle valves are suitable for high or low temperature applications. You need to specify the valve housing and packing/sealing material appropriately, especially for extreme temperatures, to ensure it can withstand the requirements. The two most common sealing materials are PTFE (Teflon) for a temperature range of -65°F to 450°F (-54° C to 232°C) and PEEK (Polyether Ether Ketone) for increased temperature resistance up to 600°F (315 °C).
Needle Valve Application
- All field analog instruments are fitted with a needle valve to control flow entry, where sudden surges of fluid under pressure can damage the instruments.
- Needle valves can be used in situations where the flow must stop gradually and in an application where precise adjustments of flow are required or where a small flow rate is desired such as sample points in the piping
- Needle valves can be used as both on/off and throttle valves
- Used in all type of industries for controlling and metering applications of fluid such as steam, air, gas, oil, water or other non-viscous liquids.