Needle valves are used to restrict and control flow rates. These valves normally consist of a body with a tapered needle within a seat. To adjust the flow rate, the needle is screwed in or out via the adjustment knob. Needle valves are very common and are available in different sizes,flow rates, sensitivities, and ports.
above Figure shows a schematic representation of a needle valve. The needle is adjusted in and out of the seat to change the effective orifice size.
above Figure shows a typical 90° needle valve with female NPT ports.