CENTRIFUGAL PUMPS

A centrifugal pump is intended to move liquid along a pipe. It does this by means of a rotating impeller which radiates the fluid outwards into a diffuser or volute chamber. The centrifugal pump is used to discharge large amounts through a small head, by means of converting kinetic energy into potential energy measurable as static fluid pressure at the outlet of the pump. A centrifugal pump may have one or more impellers. The more impellers it has in sequence then the higher the pressure that is achieved at the outlet. If it is required to achieve a higher fluid output then the impellers can be connected in parallel. However all the energy added to the fluid is due to the power of the electric or other force driving the impeller. It is vital to have correct design, installation and monitoring of the centrifugal pump or there will be a waste of energy and the pump will be inefficient.

It is important to be aware of the potential problems of centrifugal pumps. For instance if the pressure of the liquid being pumped falls below its vapor pressure that vapor bubbles can form – a process known as cavitation. If the cavitation is inertial, where a void or a bubble collapses, it produces a shock wave. This often happens in pumps, propellers and impellors and even the vascular tissues of plants. In a centrifugal pump where the cavitation is noninertial then the bubble in the fluid is forced to oscillate in size or shape. This oscillation can be caused by an external source of energy such as an acoustic field and means that the process can often be used in ultrasonic cleaning baths. However the shock waves formed by cavitation in centrifugal pumps is generally not desirable because it can be strong enough to affect and damage moving part. This means that it is a major design consideration when designing machines such as turbines and propellers and is a major field in the study of fluid dynamics.

Another problem facing centrifugal pumps is that if there are solids suspended in the liquid they are pumping then there can be wear of the impellers. Even more important if the fluid has certain corrosive properties then there may be corrosion inside the pump. Another problem is that the centrifugal pump may overheat due to low flow and unless the impeller is a tight fit to the housing there can be leakage along the rotating shaft.

In addition to the above, it is important that the centrifugal pump remains primed, - in other words it has to be filled with the fluid to be pumped in order to operate. Overall, centrifugal pumps play an important and fundamental role in many operations requiring the movement of fluids, and to be the best results the centrifugal pumps needs to be designed to be fit for the intended purpose, and also needs to be able to overcome the problems outlined above.