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To prevent the pump from cavitation, the excess energy per unit weight of liquid at the pump impeller inlet must exceed the vaporization pressure. Please see the following brief explanation: When the suction height of the centrifugal pump is too high and the liquid temperature is relatively high, causing the suction inlet pressure to be less than or equal to the saturated vapor pressure of the liquid, the liquid will boil and vaporize at the pump inlet under this environment, forming a space filled with steam in the pump casing. As the pump rotates, the bubbles enter the high-pressure area. Due to the effect of the pressure difference, the bubbles burst under pressure and re-condensate. At the moment of condensation, the particles collide with each other, generating a high local pressure. If these bubbles burst and condense near the metal surface, the liquid particles will be like countless small warheads, continuously hitting the metal surface, causing cracks on the metal surface, and even local peeling, making the impeller surface honeycomb-shaped. At the same time, some active gases in the bubbles, such as oxygen, enter the cracks on the metal surface, and use the heat released when the bubbles condense to cause the metal to be chemically corroded. The above phenomenon is called cavitation. The cavitation phenomenon of a centrifugal pump refers to the partial vaporization of the transported liquid due to the saturated vapor pressure at the delivery temperature being equal to or lower than the pressure at the pump inlet (actually the blade inlet), causing the pump to produce noise and vibration. In severe cases, the pump's flow rate, pressure head and efficiency are significantly reduced. Obviously, cavitation is not allowed to occur in the normal operation of a centrifugal pump. The key to avoiding cavitation is to install the pump at the correct height, especially when transporting volatile liquids with higher temperatures. Substitute the Hs1 value into the equation to obtain the installation height Hg=Hs1-Hf0-1=0.78-1.5=-0.72m. A negative value for Hg means that the pump should be installed below the liquid level of the pool, at least 0.72m lower than the liquid level. When cavitation occurs, the pump will produce noise and vibration, causing the pump's head, flow, and efficiency to drop sharply. At the same time, it will accelerate material damage and shorten the service life of the parts. Therefore, the suction height of the pump must be limited to prevent large amounts of liquid from vaporizing to avoid cavitation. The height between the center of the suction inlet of the pump and the liquid level of the reservoir is called the suction height. Assuming that there is an absolute vacuum at the impeller inlet, the resistance of the suction pipeline is zero, and the liquid level is a standard atmospheric pressure, then the theoretical geometric height is 10.33 meters. However, due to various resistance losses in the pump suction pipe, and the impossibility of achieving complete vacuum at the pump impeller inlet and other unfavorable factors, plus the necessary cavitation margin at the pump inlet, the suction height of a centrifugal water pump generally does not exceed 4-5 meters. The allowable suction vacuum height Hs refers to the maximum vacuum degree that can be achieved by the pressure p1 at the pump inlet. The actual allowable suction vacuum height Hs value is not a value calculated based on the formula, but a value experimentally determined by the pump manufacturer. This value is attached to the pump sample for user reference. It should be noted that the Hs value given in the pump sample is the value when clean water is used as the working medium, the operating conditions are 20°C and the pressure is 1.013×105Pa. When the operating conditions and working medium are different, conversion is required. 1) Transporting clean water, but the operating conditions are different from the experimental conditions. Hs1=Hs+(Ha-10.33)-(Hυ-0.24) can be converted according to the following formula. 2) Transporting other liquids. When the conditions of the transported liquid and the villain are different from the experimental conditions, a two-step conversion is required.: The first step is to use the above formula to determine the Hs1 detected in the pump sample. ； The second step is to convert Hs1 into H's according to the following formula: NPSH Δh For oil pumps, the NPSH Δh is used to calculate the installation height, that is, the NPSH Δh is obtained from the oil pump sample, and its value is also measured with 20°C clean water. If other liquids are transported, calibration is also required and please check the relevant books in detail. Suction lift = standard atmospheric pressure (10.33 meters) - NPSH - safety amount (0.5 meters). The standard atmospheric pressure energy pressure pipeline vacuum height is 10.33 meters. For example: The required NPSH of a certain pump is 4.0 meters. What is the suction lift Δh? untie: Δh=10.33-4.0-0.5=5.83 meters ； From a safety perspective, the actual installation height of the pump should be smaller than the calculated value. Also, when the calculated Hg is a negative value, it means that the suction inlet position of the pump should be below the liquid level of the storage tank. For example, a centrifugal pump found from the sample that the allowable vacuum height Hs=5.7m. It is known that the total resistance of the suction pipeline is 1.5mH2O, the local atmospheric pressure is 9.81×104Pa, and the dynamic pressure head of the liquid in the suction pipeline can be ignored. Trial calculation: 1) Installation of the pump when transporting clean water at 20℃ ； 2) Change to the installation height of the pump when transporting 80℃ water. untie: The installation height of the pump when transporting clean water at 20℃ is known: Hs=5.7mHf0-1=1.5mu12/2g≈0 The local atmospheric pressure is 9.81×104Pa, which is basically consistent with the experimental conditions when the pump leaves the factory, so the installation height of the pump is Hg=5.7-0-1.5=4.2m. 3) Installation height of the pump when transporting 80°C water. When transporting 80°C water, the Hs value in the pump sample cannot be directly used to calculate the installation height. Hs needs to be converted according to the following formula, that is: Hs1=Hs+(Ha-10.33)-(Hv-0.24) known: Ha=9.81×104Pa≈10mH2O. From the appendix, it is found that the saturated vapor pressure of water at 80 degrees Celsius is 47.4kPa. Hv=47.4×103Pa=4.83mH2OHs1=5.7+10-10.33-4.83+0.24=0.78m