The amount of energy given to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, then the higher will be the velocity of the liquid at the vane tip and the greaterthe energy imparted to the liquid. The kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow. When the liquid slows down in the pump casing some of the kinetic energy is converted to pressure energy. It is the resistance to the pump's flow that is read on a pressure gauge attached to the discharge line.
Pressure is a measurement of the resistance to flow.
Water is a benchmark, having a specific gravity of 1.0. Return to Table of Contents . Note that as you increase the diameter of the impeller the tip speed at the outer edge of the impeller increases commensurately. However, the total energy imparted to the liquid as the diameter increases goes up by the square of the diameter increase. This can be understood by the fact that the liquid's energy is a function of its velocity and the velocity accelerates as the liquid passes through the impeller.