In the opening of the pump string, and even the adjustment of the way: when a single pump can not meet the transfer task, can be used in parallel or series operation of the pump. Two same types of centrifugal pumps in parallel, although the pressure head changed little, but increase the total transport flow, the overall efficiency of the pump in parallel and single pump efficiency is the same; pump in series increase the total pressure head, flow changed little, the overall efficiency of the tandem pump and single pump efficiency. Two parallel pumps, flow and pressure head has improved, but due to restricted by the characteristic curve of pipeline, pipeline resistance increases, two pumps in parallel the total throughput equal to LV volume delivery pump twice. Two pumps in series, pressure head and flow rate will increase, but the total head two pumps in series is still less than two times of the original pump pressure head.
Open pump cavitation, open pump inlet pressure P1 is equal to or less than under the same temperature liquid saturation vapor pressure PV, liquid vaporization occurs, bubbles under high pressure, rapid condensation or burst produces the impact of great pressure, high frequency, strong vibration of the pump body and noise, liquid flow rate, pressure (outlet pressure) head and efficiency decreased significantly. This phenomenon is called the centrifugal pump cavitation.
In the operation of the pump (energy conversion): before the pump start, the pump shell filled with liquid is transported; after the start, the impeller shaft driven by the high-speed rotation, the liquid between the blades must also be with the rotation. Under the action of centrifugal force, liquid from the impeller center thrown toward the outer edge and get the energy, to speed away from the outer edge of the impeller in the pump shell shaped cochlea. In the spiral case, the liquid is slow down due to the gradual expansion of the flow channel, and the partial kinetic energy is changed into the static pressure energy, and finally, a high pressure is discharged into the discharge pipe to be sent to the required place. Liquid from the outer edge of the impeller center flows, in the center of the impeller formed vacuum, due to the pressure on the top of the tank liquid level is greater than the pressure pump at the entrance, the liquid will be continuous pressure into the impeller. Visible, as long as the impeller rotates, the liquid will continue to be inhaled and discharged.
