If you have ever needed to control flow precisely, not just turn it on or off, you have probably run into a needle valve.
- What Is a Needle Valve？
A válvula de aguja is a type of valve used for precise flow control.
A needle valve is different from a válvula de bola in function, for one reason: a ball valve is usually only completely opened or closed. A needle valve, however, can be set to any position, giving different amounts of fluid flow. For example, a needle valve would be turned a quarter turn to give a greater amount of fluid flow than if it were turned to half a turn. And so on. This is what makes a needle valve so ideal for controlling fluid flow. It can be used for many applications.
Even at small flow rates and high pressure, needle valves are suitable for very precise regulation. They are therefore the optimal valves for sample-taking applications and for the precise regulation of gases.
- How Does a Needle Valve Work？
The working principle is simple.
A needle valve has a threaded stem. At the end of the stem is a long, tapered point called the needle. This needle fits into a seat inside the valve body. The seat has a small opening.
When you turn the handle, the stem rotates. The threads drive the stem up or down.
Turn the handle one way. The stem moves down. The needle goes into the seat opening. The passage gets smaller and flow decreases.
Turn the handle the opposite way. The stem moves up. The needle pulls out of the seat opening. The passage gets larger and flow increases.
The needle is tapered, so the handle changes the opening by a very small amount. That is how you precisely control the flow.
Most needle valves are operated by hand using a handwheel. Some are automated with a hydraulic motor or a pneumatic actuator.
Either way, the job is the same: precise regulation of fluid flow.
- What Is a Needle Valve Used For？
Needle valves have several main jobs.
Flow regulation
Needle valves are used in chemical plants to add chemicals to reactors. In the laboratory, gas flow can be regulated for experiments. In hydraulic systems, the circuit can be slowly pressurized with a needle valve.
Instrument isolation
Needle valves are placed before pressure gauges, pressure switches and transmitters. Close the valve to isolate the instrument. Then the instrument can be serviced or calibrated without shutting down the process. Some models have a vent port. Then trapped pressure can be released before the instrument is removed.
Slow opening
In high-pressure systems, the opening of a valve can quickly cause a pressure surge or water hammer. This is a major concern as it can cause severe damage to the equipment as well as the surrounding pipes. Needle valves are often used to slowly open a line which can help prevent damage from a sudden surge in pressure.
In addition, a needle valve can be used to shut off a line or process. However, the needle valve is not designed to be used frequently to open and close a line or process. The use of a ball valve would be more suitable for frequent opening and closing of a line or process.
Where to Go from Here
- Need to pick the right needle valve for your project？ Read the Needle Valve Selection Guide
- Want to know where needle valves are used？ Read Aplicaciones y preguntas frecuentes sobre válvulas de aguja
