The many types of check valves are also divided into four groups according to the way the closure member moves onto the seat.

• Lift check

• Swing check (single and double plate)

• Tilting disc

• Diaphragm

The basic duty of these valves is to prevent back flow. However, the valves should also close fast enough to prevent the formation of a significant reverse-flow velocity, which on sudden shut-off, may introduce an undesirably high surge pressure and/or cause heavy slamming of the closure member against the seat. In addition, the closure member should remain stable in the open valve position.