Needle valves, sometimes called piston valves, are regulating valves that engineers use to fine-tune fluid flow and pressure.
Needle valves are similar in design to ball valves, but the biggest difference is the sharp, needle-shaped disc.
A needle valve has a small port and a threaded needle-shaped piston.
This arrangement allows the size of the orifice to be gradually increased or decreased to allow for precise flow regulation, although in general the needle valve is only suitable for relatively low flow velocities.
Needle valves can work manually or automatically.
Automatic needle valves are connected to a hydraulic motor or an air actuator that opens and closes the valve automatically.
When monitoring machinery, the motor or actuator will adjust the piston position according to timers or external performance data collected.
Both manual and automatic needle valves provide precise control of the flow rate.
One of the design features of most needle valves is that very little space is required for a significant number of turns to open.
This allows for accurate, precise and gradual control of the amount of liquid/gas that can pass through the valve.
In addition, it can prevent damage to gauges that may be affected by a sudden liquid/gas explosion and generally allows for better control and regulation.
Principles of operation of needle valve
Needle valves open and close perforated valves opened by a conical needle disk, which is raised and lowered by the rotation of a handwheel or by any automatic control mechanism.
Often, the base of the valve is also conical (pointed).
The valve needle piston is fully inserted into the base.
Due to this unique design, the needle valve can control the flow rate of liquids in the valve correctly and with complete accuracy.
When the handwheel is turned in one direction, the piston rises to open the valve and allow the liquid to pass through.
When the handwheel is turned in the other direction, the piston moves closer to the base to reduce the flow rate or close the valve.
Various options and sizes are available to connect it to a pipe or hose through a port connection, at the inlet and outlet.
The cap is attached to the valve housing, which can be made of various materials such as brass or stainless steel.
Uses of needle valve
Needle valves are often used as metering valves.
Measuring valves are very useful for flow control.
Needle valves are used to control flow and protect very delicate gauges against damage caused by sudden pressure of liquids and gases.
Needle valves are used in low pressure hydraulic systems, chemical processing, and other gas and liquid services.
Needle valves are used in flow measurement applications, especially when a constant, calibrated, low flow must be maintained for a period of time.
Because the flow rate is low and many turns of the valve stem are required to fully open and close, needle valves are not used for simple shut-off applications.
Small and simple needle valves are often used as vent valves in water heating applications.
One of the most common places for needle valves is to monitor the flow of gas, such as propane, in a system.
Needle valves are also sometimes used in vacuum systems to release gas in a controlled yet stable manner without high pressure.
Needle valve selection requirements
When choosing a needle valve, four main features should be considered:
construction materials
liquid pressure
The size of the opening or cone
Liquid temperature
construction materials
The construction materials of the needle valve are determined according to its application and use.
The most common materials for making needle valves are brass and stainless steel, the reason for which is their chemical resistance range.
However, other materials are available for specific applications
liquid pressure
Heavy duty needle valves can handle pressures up to 275 (4000 and 5000) psi to 413 bar at 100°F (38°C).
If higher pressures are required, such as high-pressure hydraulic applications, high-performance valves are available that can handle pressures up to 10,000 psi (689 bar) at 100°F (38°C).
Special designs are also available if a vacuum needle valve is required for low pressure control.
The size of the opening or cone
There is a wide range of needle valves with different cone sizes and orifices.
Connection ports can also be male and female ends.
The most commonly used needle valves range from 2 to 12 mm to 1/8 to 2 mm.
Ensuring the correct port and cone size ensures efficient flow of system operation with a low likelihood of wear or leakage.
Liquid temperature
Needle valves are suitable for high or low temperature applications.
For extreme temperatures, the valve housing and sealing materials should be specified appropriately to ensure the resistance of the needle valve against the requirements.
Two of the 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 degrees Celsius).
.