Introduction to the suction performance of various centrifugal pumps

The suction performance of a centrifugal pump includes the allowable suction vacuum height and the allowable cavitation margin. At atmospheric pressure, the boiling point of water is 100℃. When the water is heated to the boiling point, it will waste time and emit a large number of bubbles and vaporization. At high altitudes, the air is thin, the pressure is low, and the water is less than 100℃ will boil. So, the vaporization of water is not only related to temperature, but also to the atmospheric pressure on the sea surface. When atmospheric pressure decreases to a certain extent, water can also vaporize at room temperature. From the working principle of a centrifugal pump, it can be seen that the reason why the pump is able to suck up low liquid is due to the centrifugal force generated by the rotation of the impeller, which creates a relative vacuum at the pump inlet. The atmospheric pressure on the water surface of the suction pool causes the liquid to be sucked into the center of the impeller along the suction pipe. Under normal circumstances, the atmospheric pressure is equivalent to 10.3m. If the center of the impeller is an absolute vacuum and the head loss of the suction pipeline is not taken into account, the external atmospheric pressure can only lift the water by 10.3m. There are certain restrictions on the height of the visible pump.
Within the suction height range of the pump, the higher the installation position of the pump from the water surface, the greater the vacuum degree at the pump inlet, that is, the lower the pressure at the impeller inlet, in order to suck up water. When the pressure at the inlet of the water pump decreases to a certain extent, which is equal to the vaporization pressure of the liquid at the temperature at that time, the liquid begins to boil and vaporize, forming bubbles in the liquid flow, which are filled with steam and gases separated from the liquid. These bubbles enter the impeller along with the liquid flow, and due to the centrifugal force, the pressure of the liquid gradually increases, causing the steam in the bubbles to suddenly condense at higher pressure, causing the bubbles to disappear as an exception. Due to the exceptional speed of bubbles, the surrounding liquid rushes towards the original space occupied by the bubbles at extremely high speeds, producing a strong hydraulic impact, known as water hammer effect. The local instantaneous pressure generated by this water hammer can reach up to 10/3mpa. If the bubble adheres closely to the surface of the flow channel, over time, under the impact of this water hammer pressure, it will flow to the surface and cause serious damage. From practice, it can be seen that under the action of water hammer, honeycomb shaped damage occurs on the back of the blade inlet, so the pump is not allowed to work under cavitation conditions.