From the pumping principle of the centrifugal pump, it is known that the impeller rotating at a high speed throws water out and the middle of the impeller forms a vacuum state. A value smaller than the atmospheric pressure is called a vacuum degree, and the maximum vacuum degree is 10 meters of water column height. The degree of suction vacuum of the centrifugal pump is based on the cross-section of the inlet flange of the pump casing (connecting plate). Here, a vacuum gauge (meter) can be installed to measure the result. The pump factory is tested before the product leaves the factory. The data is measured and marked on the nameplate to provide the user with a basis for installing the pump. In the centrifugal pump series, the suction height of the vacuum is allowed to be 2.5-8.5 meters. Each pump has its own allowable value. Sometimes the centrifugal pump can not pump water, there are three reasons: First, the pump installation height is too high, beyond the allowable value of the pump suction vacuum height, so that the centrifugal pump will not be able to pump water. Followed by the centrifugal pump connected to the suction pipe is too long, more elbows, pipeline design is unreasonable, resulting in large resistance to water flow, large loss of water absorption. In other words, the water pump allows to suck up the vacuum height. A considerable part of the energy is consumed in the suction pipe. The remaining small part of the energy is insufficient to overcome the terrain height. Therefore, the centrifugal pump will not pump water. Once again, the packing seal device of the centrifugal pump structure is not well sealed, resulting in helium or water leakage. Because the outside of the pump is at atmospheric pressure, this sealing device is installed in the middle of the pump casing. If there is helium, it will destroy the vacuum in the middle of the impeller and the centrifugal pump will not pump water. In the same way, if the suction pipe of the pump is not sealed and the air is blown, the water pump will not pump water.
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