Needle flow control valves (needle valves) are two-way valves that may be opened or closed to block or adjust the flow of hydraulic fluid between; including fully on and fully off.
The needle valve consists of a sharp conical obstruction that is extended or retracted to block or allow flow. Normally designed so that the flow of fluid must make a non-straight turn inside the valve body which results in a desired loss of pressure across the valve when open which is greater than the loss across a gate valve.
