Throttle valves are commonly included with silencers and are commonly just called adjustable pneumatic silencers or flow control silencers. Adjustable pneumatic silencers are an inexpensive method for pneumatic flow control to control the speed at which air exits the valve. For example, by controlling the exhaust speed of a pneumatic cylinder you can control how quickly the piston is able to extend and/or retract. The flow rate of air is typically adjusted by rotating a knob to change the flow speed, like a needle valve. The position of the screw will increase or decrease the size of the valve orifice and thus adjust the flowrate of the air exiting the valve. Figure shows an example of a throttle valve.