DOSING PUMP Drawing Figure
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s a suction valve 42 preventing backflow from the predelivery chamber 9 into the container 16. The inlet 40 is disposed on a level, as seen from the fluid level formed in the predelivery chamber, vertically above the inlet side of the pump cylinder 2. There is further provided a return conduit 43 being as well connectable with the container 16 and comprising a pressure valve 44. The return conduit 43 is connected with the predelivery chamber 9 at an outlet 45, whereby the outlet 45 is disposed, as seen in vertical direction and relative to the new fluid level formed in the predelivery chamber, above the inlet side of the pump cylinder 2 and preferably above the inlet 40. Preferably the container 16 for dosing agent comprises a flexible bag 17 containing the dosing agent and being supported by a supporting container 18. The supporting container comprises venting holes 19. The conduits 41 and 43 are tightly connected with the interior of the flexible bag 17. In this manner there is formed a bacteria-tight connection between the conduits 41, 43 and the container for dosing agent, since no venting of the dosing agent is required. In particular for not fumigating dosing agents also a conventional container for dosing agent may be used, which is entered by air corresponding to the amount of dosing agent removed by suction. A bacteria filter may be provided in the venting hole in order to allow disinfected air to enter the container. Directly at the outlet 3 there is provided a pressure valve 20 being formed as a spring-biased ball valve in the embodiment shown. The pressure valve is connected with a connecting conduit 23 leading to a dosing point 22. The pressure valve 20 is provided as close as possible at the pump cylinder and preferably directly at the outlet thereof. An approximately horizontally formed conduit section 48 ending in the upper portion of a sump 27 branches off from the section 47 of the suction conduit 41 connecting the container 16 for dosing agent with the suction valve 42 before the suction valve 42. At its bottom 28 positioned below in vertical direction the pump cylinder 2 comprises an opening 29 leading into the interior of the sump 27 via a suction valve 30 directly adjacent to the opening 29 and a suction conduit 31. The suction conduit extends nearly down to the bottom of the sump. As shown in the FIGURE the diaphragm 11 is connected with the dosing piston, for example by means of a fastening washer 32 such that the