A type of reciprocating pump used to transfer liquids in which a flexible diaphragm is flexed to and fro. The liquid is drawn into a chamber and expelled as the diaphragm flexes. Non-return or check valves ensure that the liquid flows in the desired direction. The diaphragm provides a barrier between the liquid and the moving mechanical parts of the pump. It is a comparatively low-maintenance sealed pump and useful for transporting liquids where leakage may be a concern. They also have the ability to stall if run against too high a pressure. A double diaphragm pump is a variation that has two diaphragms that are flexed to and fro separating a wetted chamber and used where it is essential to fully safeguard against leakage. They are therefore used in the nuclear reprocessing industry, such as in the transfer of radioactive solutions.