edge thus there is a constant alternation between suction cutting off and possibly pressing away and a renewed suction cutting and so forth while at the same time a constant opening and closure of the passage openings takes place stoppages of the passage openings are effectively prevented by the thereby occurring pulsating flow the pressing away of the sucked in parts and the generation of a pulsating flow are favoured as indicated in prespective in fig4 by the fact that the basic body of the insert piece 17 as a whole receives a profiling which is adapted to the undulatory profile of the cutting fin fig4 shows such an insert piece having five undulations in accordance with the example according to fig3 in perspective representation in the form of embodiment of a pump assemblage as illustrated in fig5 which can consist in known manner of an electric motor and a pump coupled therewith which are arranged in a common housing 51 in known manner the motor shaft 53 as pump shaft on which the pump wheel 54 is arranged protrudes into the pump chamber 52 the free edges of the vanes 541 of the pump wheel 54 here move at a short distance above a spiral or rubbing plate 521 which is arranged in the bottom of the pump chamber 52 and surrounds the suction opening 55 of the pump housing into the suction opening 55 a tube piece 56 is inserted which is made conically tapering outwards in its part 561 protruding downwards beyond the bottom of the pump chamber this conical edge 561 of the tube piece 56 is profiled in undulatory form in development.