A needle valve is a particular type of valve, one which has an small port and a needle shaped plunger that moves up & down within the confines of the port. In this way, it resembles a needle inside a syringe, which is how it gets its name. The plunger can be moved up and down within the port, allowing for more precise flow control.
Some valves only have two settings which are open and closed, but a needle valve might be half-open, barely open, or fully open creating the opportunity for greater precision.
How Do Needle Valves Work?
Needle valves open and close an orifice with a tapered end that raises and lowers with the spin of a handle. Below Figure shows a needle valve cross sectional view, design, and components. The handle (A) is connected to the plunger, also called a stem (F). When you turn the handle, the plunger moves up or down based on the threads (C). The locking nut (B) prevents it from fully unscrewing. As the plunger moves down, the tapered pointed end (I) comes into contact with the valve seat to fully seal the orifice (H). Often, the valve seat is also tapered. There are various options and sizes available to connect it to a pipe or hose through the port connection (G) on the input and output. The bonnet (D) is connected to the valve housing (E), which can be made out of different materials like stainless steel.