A needle valve is a manual valve that used where continuous throttling of flow is required for regulation. Needle valves are similar to the globe valve in design with the biggest difference is the sharp needle like a disk.
Needle valves are designed to give very accurate control of flow in small diameter piping systems. They get their name from their sharp-pointed conical disc and matching seat.
Image – Swagelok
Fluid flowing through the valve turns 90 degrees and passes through an orifice. Due to needle shape disk, a certain portion of the disk will pass through seat opening before disk comes in contact with the seat, which has matching tapered design as a disk. This arrangement permits a very gradual increase or decrease in the size of the opening.
Needle valve has forged and machined body. This body can be of forged carbon steel or stainless steel depending on the services requirements. A seat can be a soft, metal or composite, same as globe valve. Normally needle valves are used in smaller sizes and are provided with either screwed or socket weld end.
All the aspect of needle valve are same as a global valve except its size and pointed needle like disk. You can refer globe valve for more detail.
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.