Valves are used to control flow for liquids, gases, or other mixtures. Diaphragm valves use air or another fluid to press a diaphragm against the bottom of the valve which shuts off flow. Gate valves slide a plate in or out of the fluid flow. A butterfly valve is similar to a throttle body in that a disc inside the valve rotates parallel or perpendicular to the flow to open or close. Pneumatic diverter valves can change flow from an inlet to two or more outlets. Ball valves rotate a ball with a hole in the middle of it to open and close, and seat valves press a seal against a valve seat. A rotary airlock traps incoming air or solids in pockets and releases them at the outlet, which is useful in vacuum and pneumatic conveying systems where a difference in pressure on either side of the valve does not allow a freely open valve.