The working principle of the multistage centrifugal pump is: relying on the high-speed rotating impeller, the liquid obtains energy under the action of inertial centrifugal force to improve the pressure. Before the pump works, the pump body and the inlet pipe must be filled with water to prevent cavitation. When the impeller rolls quickly, the blade causes the water to rotate quickly, and the rotating water flies away from the impeller under the action of centrifugal force. After the water in the pump is thrown out, the central part of the impeller forms a vacuum area. The water in Suwon is pressed into the inlet pipe through the pipe network under the action of atmospheric pressure (or water pressure).
In this way, continuous pumping can be achieved. It is worth mentioning here that before the multistage centrifugal pump is started, it must be filled with water in the pump shell before it can be started, otherwise it will cause a fever in the pump body, shock, reduced water output, and damage to the pump (referred to as "cavitation") resulting in equipment accidents! The so-called cavitation refers to: when the multi-stage centrifugal pump starts, if there is air in the pump, because the density of air is very low, the centrifugal force generated after rotation is very small, so the low pressure formed in the central area of the impeller is not enough to suction the liquid level below the pump inlet into the pump, can not transport the fluid phenomenon.
The efficiency of multistage centrifugal pump is the product of mechanical, volumetric and hydraulic efficiency. The efficiency of the pump group is the product of pump efficiency and motor efficiency. The main factors that cause the low efficiency of multistage centrifugal pump units are as follows.
1. The efficiency of the pump itself is the most fundamental influence. Under the same working premise, the efficiency of the pump may differ by more than 15%.
2. The operation condition of the multistage centrifugal pump is lower than the rated condition of the pump, and the pump efficiency is low and the energy consumption is high.
3. The efficiency of the motor remains basically unchanged in operation. Therefore, it is important to choose a high efficiency motor.
4. The influence of mechanical efficiency is mainly related to the design and manufacturing quality. After the pump is selected, the influence of late treatment is small.
5. Hydraulic loss includes hydraulic friction and local resistance loss. After the multistage centrifugal pump runs for a certain time, it will inevitably cause surface wear of impeller and guide vane, increase hydraulic loss and decrease hydraulic efficiency.
6. The volume loss of multistage centrifugal pump is also known as leakage loss, including three leakage losses of impeller sealing ring, interstage and axial force balancing mechanism. The level of volumetric efficiency is not only related to design and manufacturing, but also related to late management. After continuous operation of the pump for a certain time, the clearance increases and the volumetric efficiency decreases because of the friction between the components.
7. Because the filter cylinder is blocked, pipeline intake and other reasons, the multi-stage centrifugal pump is evacuated and idling.
8. Before the multistage centrifugal pump starts, the staff does not pay attention to the preparatory work before the multistage centrifugal pump starts, and the basic operation procedures such as warm pump, disk pump, and perfusion pump are not thoroughly implemented, often resulting in cavitation of the pump, resulting in large pump noise, large vibration, and low pump efficiency.