A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. … Liquid flows in to the pumpas the cavity on the suction side expands and the liquid flows out of the discharge because 
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 that positive displacement pumps will move fluid at the same swiftness regardless of the pressure on the inlet end and centrifugal pumps will not
