Screw style pumps generate great pressures due to the tight tolerances between the internal screw or rotor and the outer elastomer bush. These components are consumables and wear and eventually need to be replaced to maintain the pumps original performance. Wear is accelerated by pumping fluids containing solids or where the pump is allowed to run dry without water.
Replacement of these pumps is straight forward with basic hand tools. The rotor bush is sandwiched between the pump casing and a steel plate. To replace this part, remove the screws at the top of the pump which fixes the cable tie locations, this will allow the sandwich plate to easily be removed so the new bush can be fitted.
The screw itself is replaced using a reverse thread to the pump output shaft. The motor shaft can be fixed with a spanner while the old rotor is loosen in a clockwise twisting direction.