ANS:D - To increase the pump discharge rate.

The function of a volute casing in a centrifugal pump is to collect liquid from the periphery of the impeller and to transmit it to the delivery pipe at constant velocity. Therefore, the option that is not the function of a volute casing is: To increase the pump discharge rate. Explanation:

1. To reduce the head loss in discharge: The design of the volute casing helps to convert some of the kinetic energy of the fluid exiting the impeller into pressure energy, thereby reducing head loss in the discharge. This contributes to the overall efficiency of the pump.
2. To increase the pump efficiency: The volute casing plays a crucial role in optimizing the flow pattern and minimizing energy losses, which ultimately improves the efficiency of the centrifugal pump.
3. To collect liquid from the periphery of the impeller and to transmit it to the delivery pipe at constant velocity: This is the primary function of the volute casing. It collects the fluid exiting the impeller and gradually decelerates it, converting kinetic energy into pressure energy to ensure a smooth and continuous flow of liquid to the discharge pipe.
4. To increase the pump discharge rate: While the volute casing does contribute to the overall performance and efficiency of the pump, its primary function is not to directly increase the discharge rate. Instead, it ensures that the fluid is efficiently collected and discharged from the pump while maintaining a constant velocity.