Pipeline centrifugal pump installation of key technologies Centrifugal pump installation height that is suction Cheng use

First, the centrifugal key pipeline pump mounting technique is to determine the key installation techniques i.e. suction centrifugal pump installation height. This height is the vertical distance from the surface of water to a centrifugal pump impeller centerline, it allows a high degree of vacuum suction can not be confused, pump the product labeling or instructions on the vacuum suction on plate height value refers vacuum pump inlet section, But also at 1 standard atmospheric pressure, the water temperature of 20 degrees Celsius, the test was measured and determined. It does not consider the condition of the water flow after the water supply pipe is matched. The pump installation height should be allowed to suck vacuum height deducted after the head of the suction pipe loss, the remaining part of the value, it is necessary to overcome the actual terrain water absorption height. Pump installation height can not exceed the calculated value, otherwise, the centrifugal pump will not pump water. In addition, the impact of the calculated value is the size of the suction pipe lift loss lift, it is appropriate to use the shortest pipe layout, and try to install less elbow and other accessories, but also consider the appropriate with some larger diameter pipes to reduce the flow rate within the pipe.
It should be noted that the pipelines centrifugal pump installation site elevations and water temperature is different from the test conditions, such as the local elevation of 300 meters above or pumping water temperature exceeds 20 degrees Celsius, the calculated value to be amended. Ie atmospheric pressure at different elevations and saturated vapor pressure above 20 degrees Celsius. However, when the water temperature is below 20 degrees Celsius, the saturated steam pressure is negligible.
From the pipeline installation technology, water pipes require strict sealing, can not leak, leaking, otherwise it will undermine the centrifugal pump inlet at the vacuum, so that the centrifugal pump to reduce the amount of water, even in serious pumping can not come to the water. Therefore, we should conscientiously do the work of the interface of the pipeline to ensure the construction quality of pipeline connection.
Second, the installation of centrifugal pump height Hg Allowable vacuum suction height Hs refers to the pressure at the pump entrance p1 allows the maximum degree of vacuum.
The actual allowable suction height, Hs, is not a value calculated according to the equation, but a value determined experimentally by the pump manufacturer, which is attached to the pump sample for user investigation. It should be noted that the value of Hs given in the pump sample is the value of water used as working medium, operating conditions of 20 ℃ and pressure of 1.013 × 105Pa, when the operating conditions and working medium are different, need to be converted.
1 transport of water, but the operating conditions and experimental conditions are different, according to the following conversion Hs1 = Hs + Ha-10.33 - Hυ-0.24
2 Conveying Other Liquids When the condition of the liquid being transported and the villain is different from the experimental conditions, two-step conversion is required: the first step will be Hs1 detected in the pump sample according to the above formula; and the second step will convert Hs1 into H & # 900; s
2 NPSH Δh
For the oil pump, the calculation of the installation height is calculated using the cavitation allowance Δh, that is, the degree of vacuum that the pump allows to suction the liquid, that is, the allowable installation height of the pump, in meters. Naphthenic residual amount Δh by the pump in the sample, its value is also measured with 20 ℃ water. If you transfer other liquids, also need to be corrected, detailed investigation of the books.
Stroke = standard atmospheric pressure (10.33 meters) - NPSH - safe amount (0.5 meters)
Standard atmospheric pressure pipeline pressure can be 10.33 meters in height.
For example: a pump required NPSH is 4.0 meters, suction Δh?
Solution: Δh = 10.33-4.0-0.5 = 5.83 m From the safety point of view, the actual pump installation height should be less than the calculated value. When the calculated value of Hg is negative, it indicates that the suction port of the pump should be below the level of the tank.
Example 2-3 A centrifugal pump from the sample was allowed to suction on the vacuum height Hs = 5.7m. It is known that the total resistance of the suction line is 1.5 mH2O and the local atmospheric pressure is 9.81 × 10 4 Pa. The dynamic head of liquid in the suction line is negligible. Try to calculate
1 transport 20 ℃ water centrifugal pump installation;
2 instead of conveying 80 ℃ water centrifugal pump installation height.
Solution: 1 delivery of 20 ℃ water pump installation height is known: Hs = 5.7m
Hf0-1 = 1.5m
u12 / 2g≈0
The local atmospheric pressure is 9.81 × 104Pa, basically in line with the experimental conditions of the pump factory, so the installation height of the pump Hg = 5.7-0-1.5 = 4.2m.
2 When the delivery of 80 ℃ water pump installation height When the water delivery 80 ℃, can not be directly used in the pump sample Hs value to calculate the installation height, according to the following formula for Hs when the line conversion, that Hs1 = Hs + Ha-10.33 - Hυ-0.24
Ha = 9.81 × 104Pa ~ 10mH2O is known, the saturation vapor pressure of water at 80 ℃ is 47.4kPa.
Hv = 47.4 × 103 Pa = 4.83 mH2O
Hs1 = 5.7 + 10-10.33-4.83 + 0.24 = 0.78m
Hs1 value into the type to obtain the installation height Hg = Hs1-Hf0-1 = 0.78-1.5 = -0.72m
Hg is negative, indicating that the pump should be installed below the tank level, at least 0.72 m below the liquid level
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