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Centrifugal pump installation height and suction selection

1. The key installation technology of centrifugal pump

The key to the installation technology of the pipeline centrifugal pump is to determine the installation height of the centrifugal pump, that is, the suction lift. This height refers to the vertical distance from the water surface of the water source to the centerline of the impeller of the centrifugal pump. It cannot be confused with the allowable suction vacuum height. The allowable suction vacuum height marked on the pump product manual or nameplate refers to the vacuum value on the water inlet section of the pump. In addition, it was measured under the condition of 1 standard atmospheric pressure and water temperature of 20°C. It does not consider the water flow conditions after the suction pipe is matched. The installation height of the water pump should be the remaining value after deducting the loss lift of the suction pipe from the suction vacuum height, which should overcome the actual topographical suction height. The installation height of the water pump cannot exceed the calculated value, otherwise, the centrifugal pump will not be able to pump water. In addition, the influence on the calculated value is the resistance loss head of the suction pipe. Therefore, the shortest pipeline arrangement should be adopted, and fittings such as elbows should be installed as little as possible. It is also possible to consider appropriately matching larger diameter water pipes to reduce the flow rate in the pipe. It should be pointed out that when the elevation and water temperature of the pipeline centrifugal pump installation site are different from the test conditions, if the local altitude is above 300 meters or the temperature of the pumped water exceeds 20°C, the calculated value should be corrected. That is, the atmospheric pressure at different altitudes and the saturated vapor pressure when the water temperature is higher than 20°C. However, when the water temperature is below 20°C, the saturated vapor pressure is negligible. From the perspective of pipeline installation technology, the water suction pipeline requires strict sealing, no air or water leakage, otherwise it will destroy the vacuum at the water inlet of the centrifugal pump, reduce the water output of the centrifugal pump, and even fail to pump water in severe cases. Therefore, it is necessary to do a good job in the interface work of the pipeline to ensure the construction quality of the pipeline connection.

2. Calculation of installation height Hg of centrifugal pump

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 is not the value calculated according to the formula, but the value measured by the pump manufacturer's experiment. This value is attached to the pump sample for users to check. 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 condition is 20°C and the pressure is 1.013×105Pa. When the operating conditions and working medium are different, conversion is required. 1. Conveying clean water, but the operating conditions are different from the experimental conditions. It can be converted according to the following formula: Hs1=Hs+Ha-10.33 - Hυ-0.24 2. Conveying other liquids. : The first step is to convert Hs1 from the pump sample according to the above formula; the second step is to convert Hs1 into H?s according to the following formula 2 NPSH Δh For oil pumps, use NPSH Δh to calculate the installation height , that is, the vacuum degree that the pump allows to absorb liquid, that is, the installation height that the pump allows, in meters. Use NPSH Δh to check from the oil pump sample, and its value is also measured with 20°C water. If other liquids are transported, calibration is also required, please refer to related books for details. Suction lift = standard atmospheric pressure (10.33 meters) - NPSH - safety volume (0.5 meters) The standard atmospheric pressure can pressure the vacuum height of the pipeline to 10.33 meters. For example: A pump must have a NPSH of 4.0 meters, what is the suction lift Δh? Solution: Δh=10.33-4.0-0.5=5.83 meters From the perspective of safety, the actual installation height of the pump should be less than the calculated value. When the calculated Hg is a negative value, it means that the suction port of the pump should be below the liquid level of the storage tank. Example 2-3 The allowable suction vacuum height Hs=5.7m for a certain centrifugal pump is checked from the sample. 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 The installation of the centrifugal pump when delivering clean water at 20°C. 2 Change to the installation height of the centrifugal pump when transporting 80°C water. Solution: 1. The installation height of the pump when delivering clean water at 20°C. Known: Hs=5.7m Hf0-1=1.5m u12/2g≈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 . 2 m. 2 The installation height of the pump when delivering 80°C water When delivering 80°C water, the Hs value in the pump sample cannot be directly used to calculate the installation height, and the Hs should be converted according to the following formula, that is, Hs1=Hs+Ha-10.33 - Hυ-0.24 It is known that Ha=9.81×104Pa≈10mH2O, and the saturated vapor pressure of water at 80°C is found to be 47.4kPa from the appendix. Hv=47.4×103 Pa=4.83 mH2O Hs1=5.7+10-10.33-4.83+0.24=0.78m Substituting the Hs1 value into the formula to obtain the installation height Hg=Hs1-Hf0-1=0.78-1.5=-0.72m Hg is Negative value means that the pump should be installed below the liquid level of the pool, at least 0.72m lower than the liquid level. The single-stage double-suction centrifugal pump is a new type of high-efficiency energy-saving water pump. Nearly 20% higher than the original water pump. 1. Compact structure, beautiful appearance, good stability, and easy installation. 2. The optimized design of the double-suction impeller for stable operation reduces the axial force to a minimum, and has a blade shape with excellent hydraulic performance. After precision casting, the inner surface of the pump casing and the surface of the impeller are extremely bright and have significant anti-cavitation performance and high efficiency. 3. SKF and NSK bearings are used for bearings to ensure smooth operation, low noise and long service life. 4. The shaft seal is BURGMANN mechanical seal or stuffing seal. Can guarantee 8000 hours of operation without leakage. 5. The installation form does not need to be adjusted during assembly, and it can be adjusted according to the site use conditions. Standalone or horizontal installation. 6. Adding a self-priming device can realize automatic water suction, that is, no bottom valve, vacuum pump, or backfilling is required, and the pump can be started. 72m, single-stage double-suction centrifugal pump, single-stage double-suction centrifugal pump is a new type of high-efficiency energy-saving water pump. Under the same energy consumption conditions, its operating efficiency can be nearly 20% higher than that of the original water pump. 1. Compact structure, beautiful appearance, good stability, Easy to install. 2. The optimized design of the double-suction impeller for stable operation reduces the axial force to a minimum, and has a blade shape with excellent hydraulic performance. After precision casting, the inner surface of the pump casing and the surface of the impeller are extremely bright and have significant anti-cavitation performance and high efficiency. 3. SKF and NSK bearings are used for bearings to ensure smooth operation, low noise and long service life. 4. The shaft seal is BURGMANN mechanical seal or stuffing seal. Can guarantee 8000 hours of operation without leakage. 5. The installation form does not need to be adjusted during assembly, and it can be adjusted according to the site use conditions. Standalone or horizontal installation. 6. Adding a self-priming device can realize automatic water suction, that is, no bottom valve, vacuum pump, or backfilling is required, and the pump can be started. 72m, single-stage double-suction centrifugal pump, single-stage double-suction centrifugal pump is a new type of high-efficiency energy-saving water pump. Under the same energy consumption conditions, its operating efficiency can be nearly 20% higher than that of the original water pump. 1. Compact structure, beautiful appearance, good stability, Easy to install. 2. The optimized design of the double-suction impeller for stable operation reduces the axial force to a minimum, and has a blade shape with excellent hydraulic performance. After precision casting, the inner surface of the pump casing and the surface of the impeller are extremely bright and have significant anti-cavitation performance and high efficiency. 3. SKF and NSK bearings are used for bearings to ensure smooth operation, low noise and long service life. 4. The shaft seal is BURGMANN mechanical seal or stuffing seal. Can guarantee 8000 hours of operation without leakage. 5. The installation form does not need to be adjusted during assembly, and it can be adjusted according to the site use conditions. Standalone or horizontal installation. 6. Adding a self-priming device can realize automatic water suction, that is, no bottom valve, vacuum pump, or backfilling is required, and the pump can be started.