A positive displacement pump makes a liquid move by trapping a fixed amount and forcing (displacing) that trapped volume in to the discharge pipe. … Liquid flows in to the pumpas the cavity on the suction part expands and the liquid flows out of the discharge because the cavity decreases.

The most common type among centrifugal pump is the radial flow pump. … The main difference between these kinds of pumps and centrifugal is usually that positive displacement pumps will move fluid at the same speed regardless of the pressure on the inlet end and centrifugal pumps won’t