Abstract: In a diaphragm pump including a first chamber for liquid to be pumped separated from a second chamber for drive fluid by a diaphragm which is driven by a piston alternatively placing the drive fluid under pressure and releasing the pressure from the drive fluid, a signal generator or magnet is located in the diaphragm while a signal detector is located within the pump housing to enable detection of displacement of the diaphragm and, accordingly, the displaced volume of the diaphragm pump. Detection of the displaced volume is used by a regulator to generate a drive signal which, in turn, is used to drive a motor operator connected to a pressure relief valve to control drive fluid pressure and, accordingly, the displaced volume.