Abstract: In the case of a diaphragm pump, as is more particularly used for dosing or metering liquids and which is provided on the one hand with a dosing chamber with a suction and pressure valve and on the other with a hydraulic working chamber with drive piston and pressure relief valve, both chambers being separated by the working diaphragm, an effective diaphragm protection against excessive deflection and consequently overstressing is obtained in that the diaphragm defines a chamber connected to the working chamber by means of at least one overflow channel and in the vicinity of the overflow channel is guided a valve unit comprising a tappet with in each case one valve disk for the facing openings of the overflow channel and which is in operative connection with the diaphragm.