My answer to What are the different types of losses in pump?
Answer by Arûn Râinâ:
A pump can be defined as “a mechanical device that adds energy to a fluid to increase its flow rate and static pressure.This process can be accomplished with positive displacement pumps or kinetic-energy pumps.
Losses in a Centrifugal Pump
• Mechanical friction power loss due to friction between the fixed and rotating parts in the bearing and stuffing boxes.
• Disc friction power loss due to friction between the rotating faces of the impeller (or disc) and the liquid.
• Leakage and recirculation power loss. This is due to loss of liquid from the pump and recirculation of the liquid in the impeller. The pressure difference between impeller tip and eye can cause a recirculation of a small volume of liquid, thus reducing the flow rate at outlet of the impeller
Head losses are potential energy that has been lost because of frictional resistance of the piping system (pipe, valves, fittings, and entrance and exit losses). Unlike velocity head, friction head cannot be ignored in system calculations. Head loss values vary as the square of the flow rate. Head losses can be a significant portion of the total head.
Control losses occur on the discharge side of a centrifugal pump that has been equipped with a back pressure valve to control flow rate. As the liquid flows through the control valve, energy is lost. Next to static head, control losses are frequently the most important factor in calculating the pump’s total dynamic head. For pump applications, control losses are treated separately from head losses, even though they are included in the hf term.