Selection of installation height and suction stroke of sanitary negative pressure pump

1. The key installation technology of sanitary 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 centrifugal pump impeller. It cannot be confused with the allowable suction vacuum height. The allowable suction vacuum height indicated on the pump product manual or nameplate refers to the vacuum value on the section of the water inlet of the pump. And it is measured under 1 standard atmospheric pressure and 20°C water temperature. It does not consider the water flow after the suction pipe is installed. The installation height of the water pump should be the value of the remaining part of the value after the vacuum height is allowed to suck up and the loss of the suction pipe is deducted. It must overcome the actual topographic water absorption height. The installation height of the pump should not exceed the calculated value, otherwise, the centrifugal pump will not be able to pump water. In addition, the magnitude that affects the calculated value is the resistance loss head of the suction pipe. Therefore, it is advisable to adopt the shortest pipeline layout and install as few fittings as elbows. It is also possible to consider appropriately matching larger diameter water pipes to reduce the flow velocity 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 water temperature of the pumped water exceeds 20°C, the calculated value must be corrected. That is, the atmospheric pressure at different altitudes and the saturated steam 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 or water leakage, otherwise it will destroy the vacuum at the 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 quality of the pipeline connection.

2. Calculation of installation height Hg of sanitary negative pressure pump

　　The allowable vacuum height Hs refers to the maximum vacuum that can be reached by the pressure p1 at the inlet of the pump. The actual allowable suction vacuum height Hs value is not a value calculated according to the formula, but a value determined experimentally 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, and the operating condition is 20℃ 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, 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 to H?s 2 according to the following formula. Cavitation allowance Δh For oil pumps, use the cavitation allowance Δh to calculate the installation height , That is, the degree of vacuum that the pump allows to suck liquid, that is, the allowable installation height of the pump, in meters. Use the NPSH Δh to check from the oil pump sample, and its value is also measured with 20℃ clean water. If other liquids are to be transported, calibration is also required, and the relevant books should be checked in detail. Suction range = standard atmospheric pressure (10.33 meters)-cavitation margin-safety amount (0.5 meters) The vacuum height of the standard atmospheric pressure energy pressure pipeline is 10.33 meters. For example: a certain pump must have a NPSH of 4.0 meters, what is the suction stroke 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 negative, it means that the suction port of the pump should be below the liquid level of the storage tank. Example 2-3 A centrifugal pump found from the sample that the allowable suction vacuum height is 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 is negligible. Trial calculation: 1 Installation of centrifugal pump when delivering 20℃ clean water. 2 Change to the installation height of the centrifugal pump when delivering 80℃ 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 in line 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 used to calculate the installation height. The following formula is required to convert the Hs time, that is, Hs1 = Hs + Ha－10.33 － Hυ－0.24. Knowing Ha=9.81×104Pa≈10mH2O, the saturated vapor pressure of 80℃ water 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 Substituting the Hs1 value 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 pumps and single-stage double-suction centrifugal pumps are new high-efficiency and energy-saving water pumps. Under the same energy consumption conditions, their operating efficiency can be It is nearly 20% higher than the original water pump. 1. Compact structure, beautiful appearance, good stability and easy installation. 2. Smooth operation and optimized design of the double-suction impeller to minimize the axial force, and the blade shape with excellent hydraulic performance, and through 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. The bearings are selected from SKF and NSK bearings to ensure stable operation, low noise and long service life. 4. The shaft seal uses BURGMANN mechanical seal or packing seal. It can guarantee 8000 hours of operation without leakage. 5. The installation form does not need to be adjusted during assembly, and it can be used according to the site conditions. Discrete or horizontal installation. 6. The installation of self-priming device can realize automatic water suction, that is, there is no need to install a bottom valve, no vacuum pump, no backfilling, 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 and 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. Smooth operation and optimized design of the double-suction impeller to minimize the axial force, and the blade shape with excellent hydraulic performance, and through 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. The bearings are selected from SKF and NSK bearings to ensure stable operation, low noise and long service life. 4. The shaft seal uses BURGMANN mechanical seal or packing seal. It can guarantee 8000 hours of operation without leakage. 5. The installation form does not need to be adjusted during assembly, and it can be used according to the site conditions. Discrete or horizontal installation. 6. The installation of self-priming device can realize automatic water suction, that is, there is no need to install a bottom valve, no vacuum pump, no backfilling, 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 and 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. Smooth operation and optimized design of the double-suction impeller to minimize the axial force, and the blade shape with excellent hydraulic performance, and through 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. The bearings are selected from SKF and NSK bearings to ensure stable operation, low noise and long service life. 4. The shaft seal uses BURGMANN mechanical seal or packing seal. It can guarantee 8000 hours of operation without leakage. 5. Installation mode does not need to be adjusted when assembling, it can be based on the on-site use conditions. Discrete or horizontal installation. 6. The installation of self-priming device can realize automatic water suction, that is, there is no need to install a bottom valve, no vacuum pump, no backfilling, and the pump can be started.