Patent ID: 8197192

Claim:
A pump for pumping contaminated liquid including large pieces of solid matter, comprising an open impeller ( 1 ), which is rotatable in a pump chamber of said pump, the impeller ( 1 ) being movable in the axial direction in relation to a seal housing cover ( 3 ) between a first position adjacent to an impeller seat ( 2 ) and a second position spaced apart from said impeller seat ( 2 ), said pump also comprising a cavity ( 17 ) defined by the seal housing cover ( 3 ) and the impeller ( 1 ), and at least one radial opening gap ( 20 ) connecting said cavity and said pump chamber, wherein said opening gap ( 20 ) has a first flow area when the impeller ( 1 ), in the normal operation of the pump is in the first position, and a second flow area bigger than said first flow area when the impeller ( 1 ) is spaced apart from said first position.