Abstract: A diaphragm pump having a pump chamber divided into two portions by a diaphragm of elastomeric material which is generally of hemispherical shape and clamped at its periphery in the pump chamber. The portion of the chamber including the interior of the diaphragm communicates with a cylinder in which a piston is reciprocated by rotation of a drive shaft. The pump chamber includes inlet and outlet non-return valves for the fluid to be pumped, is detachable as a unit from a housing containing the piston and cylinder and is positioned below a normally horizontal plane containing the axes of the cylinder and drive shaft.