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