The piston pump can be defined as it is a positive displacement pump. These pumps use a piston, diaphragm, otherwise plunger for moving liquids. These pumps use check valves as the input and output valves. The general piston-pump is a rotary pump which uses a wheel or revolving shaft for operating the piston.http://www.oilmaxhydraulic.com..../hydraulic-pumps-par