As impeller pumps are dry self-priming they need not be filled with liquid before starting an operation. That is a great advantage compared to other pump types, but in the same time it requires the user’s attention to prevent the pump from damage when priming air instead of liquid for a longer time.
Zuwa impeller pumps may run dry up to one minute without problems. But when the pump works without liquid for a longer time the flexible rubber wheel will be damaged. This happens frequently when emptying containers down to the last drop. Fuel oil tanks for example need to be drained completely for cleaning. It is nearly unevitable in this case, that at the end of the operation the pump takes in a great amount of air.
The dry run protection consists of a temperature probe attached to the pump cover interrupting the power supply and switching the pump off when a certain temperature limit is exceeded. A reset button starts the pump again after cooling down or eliminating the reason for the malfunction.