A positive displacement pump makes a fluid move by trapping a set amount and forcing (displacing) that trapped volume into the discharge pipe. … Liquid flows into the pumpas the cavity on the suction part expands and the liquid flows out of the discharge as the cavity decreases.
The most typical type among centrifugal pump is the radial flow pump. … The primary difference between these types of pumps and centrifugal is usually that positive displacement 
pumps will move liquid at the same rate regardless of the strain on the inlet end and centrifugal pumps will not