A centrifugal drainage pump is disclosed in the present invention, which comprising a pump body, a permanent magnet rotor, a rotor shaft, a pump cover, shaft sleeve and an impeller. A holding chamber for holding the shaft sleeve is arranged in the center of the impeller. The shaft sleeve includes a tubular body with a starting rib extruding laterally from it. A stopping rib extrudes inwardly from the internal wall of the holding chamber of the impeller. The starting rib can interfere with the stopping rib. Among pairs of interference contact surfaces between the stopping rib and the stopping rib, at least one of each pair of interference contact surfaces has a recessed notch extending axially, and the open-end of the notch is narrower than the inner space of the notch. A shock absorbing pad has a convex ridge extruding from its side that contacts with the interference contact surface. The convex ridge fits with the notch by embedding the convex ridge in the notch so that the shock absorbing pad tightly contacts with the stopping rib or starting rib. The pump can be started free of load to avoid the problem of overload during start-up of the pump. It will be easier to install the shock absorbing pad in or replace it from the starting rib and the stopping rib.
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