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