A positive displacement pump makes a fluid 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 from the discharge since the cavity decreases.
The most common type among centrifugal pump may be the radial flow pump. … The primary difference between these types of pumps and centrifugal is definitely that positive displacement pumps will move fluid at the same acceleration regardless of the pressure on the inlet end and centrifugal pumps will not
