The pump casing of a centrifugal pump is usually cast into a volute shape. The volute-shaped flow passage is continuously increased in the direction of the outflow, so that the velocity of the water flow therein can be kept constant to reduce the energy loss due to the change in the flow velocity. There is a diffused conical tube at the water outlet of the pump. As the cross section increases, the velocity gradually decreases, and the pressure gradually increases, and the kinetic energy of the water is converted into potential energy. Generally, a screw hole for venting or adding water is provided at the top of the pump body to be used for vacuuming or watering before the pump is started.
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