Centrifugal pump is a type of pump that transport liquid by centrifugal force which is developed by a high speed revolving device known as impeller. The operating principle of a centrifugal pump is shown as Figure 1 Centrifugal Pump Operating Principle. An impeller is fixed onto the pump shaft driven by a motor. A suction flange is connected with a suction pipe. The liquid is sucked into the pump through a foot valve and the suction pipe.Before starting the pump, there is full of liquid being pumped in the pump casing. As soon as the pump is operating, the impeller is driven by a motor to rotate at a high speed. The liquid between impeller blades moves with the impeller in high speed. Under the impact of the centrifugal force, the liquid is accelerated to the out rim of the impeller to gain kinetic energy and gets into the volute of the pump which converts kinetic energy into pressure by slowing down the speed of liquid. The liquid gets into the delivery pipe with a high pressure under the impact of which the liquid can be delivered to other place.
After the liquid is moved to the out rim of the impeller, a vacuum is formed in the center of the impeller. Therefore, the atmosphere pressure on the liquid tank is greater than the pressure inside the pump casing. The liquid is pressed into the casing continuously. As long as the impeller is operating, the liquid can be sucked into and discharged out of the pump continuously. Two independent characteristics define the operation of a centrifugal pump. One is the pump head characteristic curve. The other is system curve (or pipeline resistance curve). Figure 2 shows the pump head characteristic curve and the pipeline characteristic curve.Head characteristic is the relationship between the head and capacity of a centrifugal pump at a certain speed under the condition that the discharge value opening is unchanged. As shown in Figure 2, an increase in rate of low can lead to a head decrease. Under the condition that the valve opening and pump speed are unchanged, the flow of flow mainly depends on the water demand. Therefore, head characteristic reflects the relationship between the head and the flow rate of water demand.