How does a Centrifugal pump work ?


Centrifugal pumps are the most preferred
pumping devices in the hydraulic world. In this video we will have a conceptual
overview of working of centrifugal pumps. At the heart of the system lies the
impeller. It has got a series of curved vanes, fitted inside shroud plates. The impeller is always immersed in water. When the impeller is made to rotate, it makes the fluid surrounding it also
rotate. This imparts centrifugal force to the water
particles and the water moves radially out. Since rotational mechanical energy is transferred to the fluid, at discharge side of the impeller, both pressure and kinetic energy water will rise. At the suction side water is getting
displaced, so a negative pressure will be induced
at the eye. Such a low pressure helps in sucking freshwater stream into the system again. and this process continues. This is the reason why priming is
important for centrifugal pumps. If no water is present initially. the negative pressure developed by the rotating air at the Eye of impeller will be negligibly small to suck fresh stream of water. Impeller is fitted inside a casing. So the water moving out will be
collected inside it, and will move in the same direction of
rotation of impeller, to the discharge nozzle. Here you can note one speciality of casing. It has got increasing area along the flow
direction. Such increasing area will help in
accommodating, newly added water stream and will also help in reducing exit flow velocity. Reduction in flow velocity will result in increase in static pressure, which is required to overcome resistance of pumping system Here you can see more details of veins
inside impeller. They are backward curved vanes with state-of-the-art Eye configuration This vane is extracted from a KIRLOSKAR
pump model. If pressure at suction side impeller
goes below vapor pressure of water, a dangerous phenomenon could happen. Water will start to boil forming vapor
bubbles and spoil impeller materials over time This phenomenon is known as cavitation. More the section head, lesser should be
the pressure at the suction side, to lift the water. This fact puts a limit to maximum
suction head a pump can have. Careful pump selection is required to avoid the problem of cavitation. The current impeller type is enclosed, semi-open and open impellers are also in use depending upon the application. If the working fluid is cloggy in
nature, it is preferred to use open kind of impeller. But they are slightly less efficient. Mechanical design of centrifugal pump is always challenging. A shaft is used to connect between the
impeller and motor Since water pressure inside the casing is huge, a proper sealing arrangement is imperative in arresting water leakage
through the shaft-casing clearance. Mechanical seal or stuffing box based
mechanism is used for this purpose. Impeller is mounted on bearings, but at the suction side impeller, it is not advisable to fit a bearing, since it will block the flow. So bearings have to be fitted at the
other end. This means impeller is mounted like a cantilever. For high flow rate pumps, a bearing housing with cooling oil is necessary for improving the life for bearings. We thank KIRLOSKAR bothers for their technical support, in creation of
this video.