through the casing part 19 and the pump upper part 26 toward the central support body 29 located above the pump diaphragm 30 are provided at the encircling groove 25 in the cylindrical casing part 19 for the purpose of supplying and discharging the reducing agent the passages 37 38 are flow connected through the gap 39 between pressure sensor element 31 and central support body 29 chambers which are not indicated in more detail and in which non return valves 40 41 are disposed are provided in the passages 37 38 within the pump upper part 26 these non return valves 40 41 in each case include in the usual way a ball and a spring element acting on the ball so that the corresponding passage is opened or closed under the influence of the movement of the pump diaphragm 30 outside the casing part 19 the passages 37 38 end in connection pieces 42 onto which non illustrated hose lines are fitted one hose line leading through a filter to the reducing agent storage tank and the other hose line leading to the metering valve the direction of flow of the reducing agent through the diaphragm pump is indicated in the figure by arrow symbols the text that follows explains the function of the diaphragm pump with the integrated pressure sensor the armature plate 33 and through the drive shaft 32 the central support body 29 are attracted by the electromagnet 22 23 counter to the force of the coil spring 35 by a current pulse of defined length this increases the volume above the pump diaphragm 30 and reducing.