Inhalation properties include allowing the suction vacuum height and allowing the NPSH, the boiling point of water at atmospheric pressure is 100.c, the water heated to the boiling point, the water on the point, the emergence of a large number of bubbles and gasification. Thin air at high altitude, low pressure, less than 100 water. c will boil. Therefore, the vaporization of water is not only related to temperature, atmospheric pressure on the surface of the sea. When the atmospheric pressure is reduced to a certain extent, water can also be gasified at normal temperature. From the working principle of the centrifugal pump we can see that the reason why the pump can absorb the liquid from the lower is due to centrifugal force impeller rotation is generated at the pump inlet relative vacuum while the water pressure on the surface of the pool to make the liquid along the inhalation Tube inhalation impeller center. Under normal circumstances, the atmospheric pressure is equivalent to 10.3m. (The height of the sea wave is zero). If the center of the impeller is an absolute vacuum and does not account for the head loss of the suction pipe, the outside atmospheric pressure can only lift the water up to 10.3m. Visible pump height is a certain limit. Â In the pump suction height range, the higher the pump mounting position is from the water, the greater the vacuum required for the pump inlet, which is the lower pressure at the impeller inlet to draw water up. When the pressure at the inlet of the pump is reduced to a certain degree, equal to the vapor pressure at the current temperature of the liquid, the liquid begins to boil and vaporize, forming bubbles in the liquid stream, which are filled with steam and gases that have separated from the liquid. These bubbles enter the impeller together with the flow. Due to the centrifugal force, the pressure of the liquid gradually increases, causing the vapor in the bubble to suddenly condense at a higher pressure. The bubble disappears without any exception. As the bubble exception is very fast, so the liquid around the bubble at high speed into the original space occupied by the bubble, resulting in a strong water impact, that water hammer effect. This water hammer produces localized transient pressures up to 10 / 3mpa. If air bubbles cling to the surface of the runner, over time, flowing to the surface can cause serious damage under the impact of the water hammer pressure. It is known from practice that honeycomb-like damage occurs on the back of the blade inlet under water hammer action and therefore, the pump is not allowed to work under cavitation.