Abstract: An eccentric screw pump comprising an outer part (2) and an inner part (3) therein, one of the parts (2, 3) being driven rotatably and the other part (2, 3) being able to move eccentrically relative to the other part (3, 2). The screwthreads (5a, 5b) of the outer part (2) extend angularly over less than an entire helix along the axial length (L) of the part, so that during operation pumping chambers that are open to both ends are created, through which sudden pressure relief takes place.

Abstract: An eccentric screw pump comprising an outer part (2) and an inner part (3) therein, one of the parts (2, 3) being driven rotatably and the other part (2, 3) being able to move eccentrically relative to the other part (3, 2). The screwthreads (5a, 5b) of the outer part (2) extend angularly over less than an entire helix along the axial length (L) of the part, so that during operation pumping chambers that are open to both ends are created, through which sudden pressure relief takes place.

Abstract: A grinder pump has a housing having a bottom wall formed with an intake port, a drive shaft rotatable in the housing about an axis and projecting axially through the bottom wall, and a pump in the housing having a rotor connected to the shaft and operable to draw liquids and comminuted solids in through the port. A cutter head outside the housing at the bottom wall carries a blade juxtaposed with the bottom wall. The cutter head is fixed on and rotatable with the shaft for comminuting solids drawn into the intake port. An annular shield wall projects axially from the bottom wall around the cutter head and is formed with at least one axially projecting bump forming a valley constituting an intake opening through which liquid and solids can be drawn to the intake port by the pump.