DOSING PUMP Drawing Figure
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diaphragm is displaced by the upward and downward movement, resp., of the dosing piston. At the displacement of the diaphragm 11 upwardly from the lower dead centre in the first stroke the air within the suction system is sucked off and thereby the dosing agent is delivered from the flexible bag 17 into the predelivery chamber 9. With the lifting of the diaphragm 11 the dosing piston 4 is emerged from the pump cylinder 2 such that a part of the delivered dosing agent completely covers the pump cylinder 2 and an excess 32' of dosing agent remains within the predelivery chamber 9. The dosing is performed at the downward movement of pump piston 4 and diaphragm 11 and the major part of the dosing agent still present within the predelivery chamber is delivered back into the container 16 for dosing agent through the return conduit 43. A portion 32' of the predelivered amount of dosing agent remains above the dosing piston 4, because the outlet 45 is in vertical direction on a higher level than the upper inlet of the pump cylinder 2. The difference of level between the outlet 45 and the inlet of the pump cylinder is selected such that a desired portion of the pump cylinder surface always remains within the delivered dosing amount in order to avoid the formation of an incrustation at the dosing piston 4. During the suction of dosing fluid the sump 27 is permanently filled with dosing agent. At the upward movement of the dosing piston 4 the dosing agent is sucked from the sump 27 through the suction conduit 31 and the suction valve 30 into the pump cylinder 2 such that in this chamber an evacuation leading to a crystallization or polymerisation is avoided. The size of the sump is selected such that at the suction there always remains sufficient fluid and air pulsating in the conduit 41 during the operation is prevented from entering into the suction valve 30 of the dosing pump