A diaphragm pump for a seat adjusting device comprises a diaphragm and a valve member which define a pump chamber therebetween. An inlet valve and an outlet valve are formed on the valve member. A pressure chamber is in fluid communication with the outlet valve and receives fluid discharged from the pump chamber via the outlet valve. One of the diaphragm and the valve member comprises a valve membrane of a pressure relief valve integrated in the pump. The valve membrane is integrally formed with the one of the diaphragm and the valve member. The valve membrane is moveable between a first configuration in which the valve membrane closes a pressure relief channel and a second configuration in which the valve membrane opens the pressure relief channel to allow fluid to be discharged from the pressure chamber.