| 摘要 |
A positive-displacement pump (lifting pump) comprises a pump housing with a pump chamber having an inlet and an outlet passage controlled by an outlet check valve; a displacement member which delimits the pump chamber in one direction of movement of the displacement member and which is reciprocable in the pump chamber within a stroke region and includes a second check valve opening into the pump chamber within a stroke region and includes a second check valve opening into the pump chamber and disposed in a passage between the inlet and the pump chamber; and an actuating mechanism for repetitively reciprocating the displacement member in the pump housing within the stoke region. The displacement member has an upper thrust surface, which is constantly subjected to the pressure in the outlet passage during the movement of the displacement member within the stroke region, and a corresponding lower thrust surface, which is constantly subjected to the pressure in the inlet during the movement of the displacement member within the stroke region, so that the displacement member is subjected to a resulting vertical thrust force when the pressures in the inlet and the outlet are dissimilar. The pump chamber is limited in the opposite direction of movement of the displacement member by and end part, which is in engagement with the pump housing and drivable away from the pump housing by means of the displacement member upon movement of the displacement member beyond the stroke region.
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