A positive displacement pump makes a fluid move by trapping a set amount and forcing (displacing) that trapped volume in to the discharge pipe. … Liquid flows into the pumpas the cavity on the suction part expands and the liquid flows from the discharge as the cavity decreases.
The most typical type among centrifugal pump may be the radial flow 
pump. … The main difference between these types of pumps and centrifugal is definitely that positive displacement pumps will move liquid at the same acceleration regardless of the strain on the inlet end and centrifugal pumps won’t