(also called membrane pump), a pump in which the role of the piston is played by a flexible plate or diaphragm that is fastened at its periphery and is flexed by the action of a lever mechanism or by variations in the ambient pressure. Deflection of the diaphragm in one direction causes suction of the liquid being pumped; deflection in the opposite direction applies pressure to the liquid. Diaphragm pumps are used in conveying water that contains an admixture of soil (so-called frog pumps) and in conveying chemically active or flammable liquids.