The mechanism to control flow can vary based on the application of the valve. In general, there are two means of controlling flow through a valve.
Linear motion valves use a closure member that moves in a straight line to allow, stop or throttle the flow. The closure device could be a disc, slat or flexible material, like a diaphragm. The closure device can be used to:
Move a disc or plug into or against an orifice
Slide a slat, cylindrical, or spherical surface across an orifice
Move a flexible material into the flow passage
Rotary motion valves rotate a disc or ellipse about an angular or circular shaft extending across the diameter of an orifice. Quarter turn valves will be in their fully open or fully closed state after a 90° turn of the stem.