Before operating the pump it must be filled with fluid, after filling it is self-priming.

When the pump is switched on the paddle wheel transports the fluid from the suction side to the discharge side. The pump chamber increases in size internally, which results in a pressure drop, and the fluid is drawn in (Fig. 1 and Fig. 2).

On the discharge side the pump chamber reduces in size, the over pressure forces the fluid into the discharge-line (Fig. 3).