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 stroke. This height refers to the vertical distance from the water surface of the water source to the center line of the impeller of the centrifugal pump. It cannot be confused with the allowable suction suction height. The allowable suction suction height indicated 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 by conducting tests under 1 standard atmosphere and a water temperature of 20°C. It does not take into account the water flow conditions after the suction pipe is matched. The installation height of the water pump should be the remaining part of the value after the vacuum height is allowed to deduct the loss of the suction pipe, and it must overcome the actual terrain water absorption 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 size that affects the calculated value is the resistance loss head of the suction pipe. Therefore, the shortest pipeline layout should be used, and fittings such as elbows should be installed as little as possible, and a larger diameter water pipe can also be considered to reduce the flow velocity in the pipe. It should be pointed out that when the elevation and water temperature of the installation site of the pipeline centrifugal pump are different from the test conditions, such as the local altitude is more than 300 meters or the temperature of the pumped water exceeds 20℃, 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 steam pressure is negligible. From the perspective of pipeline installation technology, the suction pipeline requires strict sealing, and no air leakage or water leakage, otherwise it will destroy the vacuum degree 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 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 that the pressure p1 at the pump inlet can be allowed to achieve. The actual allowable suction vacuum height Hs value is not the value calculated according to the formula, but the value measured by the pump manufacturer. 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, it needs to be converted. 1. Transporting 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. Transporting other liquids When the conditions of the liquid to be transported and the villain are different from the experimental conditions, a two-step conversion is required : 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 2 NPSH Δh according to the following formula. For the oil pump, use the NPSH Δh to calculate the installation height , that is, the vacuum degree that the pump allows to absorb the liquid, that is, the allowable installation height of the pump, in meters. The NPSH Δh is checked from the oil pump sample, and its value is also measured with clean water at 20°C. If other liquids are transported, calibration is also required, please check the relevant books for details. Suction lift = standard atmospheric pressure (10.33 meters) - NPSH - safety amount (0.5 meters) The vacuum height of the standard atmospheric pressure energy pressure pipeline is 10.33 meters. For example: a pump must have a NPSH of 4.0 meters, find the suction lift Δh? Solution: Δh=10.33-4.0-0.5=5.83 meters From a safety point of view, 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 position of the suction port of the pump should be below the liquid level of the storage tank. Example 2-3 A centrifugal pump found the allowable suction height Hs=5.7m 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. Installation of centrifugal pump when conveying 20℃ clean water. 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 20°C clean water. 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 of the pump when it 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 transporting 80°C water When transporting 80°C water, the Hs value in the pump sample cannot be used to calculate the installation height, and the Hs time must be converted by the following formula, that is, Hs1=Hs+Ha-10.33 - Hυ-0.24 Knowing that Ha=9.81×104Pa≈10mH2O, the saturated vapor pressure of water at 80℃ is 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 Substitute the value of Hs1 into the formula to obtain the installation height Hg=Hs1-Hf0-1=0.78-1.5=-0.72m Hg is A 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. Single-stage double-suction centrifugal pump and single-stage double-suction centrifugal pump are new high-efficiency and energy-saving pumps. It is nearly 20% higher than the original water pump. 1. Compact structure, beautiful appearance, good stability and easy installation. 2. The double-suction impeller with stable operation and optimized design reduces the axial force to a minimum, and the blade shape with excellent hydraulic performance is precision cast, and the inner surface of the pump casing and the surface of the impeller are extremely bright and have remarkable anti-cavitation performance. and high efficiency. 3. Bearings SKF and NSK bearings are selected to ensure smooth operation, low noise and long service life. 4. Shaft seal Select BURGANN mechanical seal or packing seal. It can guarantee 8000 hours of operation without leakage. 5. Installation form There is no need to adjust when assembling, it can be used according to the site conditions. Discrete or horizontal installation. 6. The self-priming device is installed, which can realize automatic water absorption, that is, no bottom valve, no vacuum pump, and no inversion, and the pump can be started.