A diaphragm pump (5) for a seat adjusting device comprises a diaphragm (12) and a valve member (13, 14) which define a pump chamber (40) therebetween. An inlet valve (41) and an outlet valve (42) are formed on the valve member (13, 14). A pressure chamber (43) is in fluid communication with the outlet valve (42) and receives fluid discharged from the pump chamber (40) via the outlet valve (42). One of the diaphragm (12) and the valve member (53, 54) comprises a valve membrane (31) of a pressure relief valve integrated in the pump (5). The valve membrane (31) is integrally formed with the one of the diaphragm (12) and the valve member. The valve membrane (31) is moveable between a first configuration in which the valve membrane (31) closes a pressure relief channel and a second configuration in which the valve membrane (31) opens the pressure relief channel to allow fluid to be discharged from the pressure chamber (43).