Pumps are classified as either “kinetic” or “positive displacement” pumps. In a kinetic pump, energy is added continuously to increase the fluid’s velocity within the pump to values in excess of those that exist inthe discharge pipe. Passageways in the pump then reduce the velocity until it matches that in the discharge pipe. From Bernoulli’s law, as the velocity head of the fluid is reduced, the pressure head must increase. Therefore, in a kinetic pump the kinetic or velocity energy of the fluid is first increased and then converted to potential or pressure energy. Almost all kinetic pumps used in production facilities are centrifugal pumps in which the kinetic energy is imparted to the fluid by a rotating impeller generating centrifugal force.
In a positive displacement pump the volume containing the liquid is decreased until the resulting liquid pressure is equal to the pressure in the discharge system. That is, the liquid is compressed mechanically, causing a direct rise in potential energy. Most positive displacement pumps are reciprocating pumps where the displacement is accomplished by linear motion of a piston in a cylinder. Rotary pumps are another common type of positive displacement pump, where the displacement is caused by circular
Categories: Pumps | Tags: positive displacement, pump | Leave a comment