A displacement pump of the blade or vane type comprising a rotor with two blades, said rotor being eccentrically mounted in the casing of the pump. The rotor with its blades provides for a first pumping effect so as to transport material in first partial volumes with a first pulsating characteristic having two maxima and two minima for every full rotation of the rotor. The rotor is constructed with circumferential sections between the blades, said sections being located inside the smallest circumscribed circle of the cross-section of the pump and uniformly merging with remaining circumferences of the rotor. Between the outlet and the inlet of the pump a pivotable flap is arranged. The flap with its front edge slidingly abuts against said circumferential sections of the rotor for thereby inducing a second pumping effect. This second pumping effect has a second pulsating characteristic also having two maxima and minima for every full rotation of the rotor. The maxima of said second pulsating characteristic coincide with the minima of said first pulsating characteristic, and the minima of said second characteristic coincide with the maxima of said first pulsating characteristic, for thereby providing a pump which yields a greater total pump capacity and gives a more even total supply characteristic.
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