First, the key to installing centrifugal pump technology
Pipeline centrifugal pump installation technology key lies in determining the pump installation height (ie suction). This height is the vertical distance from the water surface to the pump impeller centerline, it allows a high degree of vacuum suction can not be confused, pump the product label instructions on the nameplate or vacuum suction on the vacuum pump height is the value at the inlet section, and Is measured at 1 standard atmospheric pressure, the water temperature of 20 degrees Celsius, the test and measured. 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 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 pipe installation techniques , the suction pipes require stringent tightness, can not leak, the leakage would otherwise damage the pump inlet at the degree of vacuum to reduce the water so that the pump, even when serious no water to pump. Therefore, we should conscientiously do the work of the interface of the pipeline to ensure the construction quality of pipeline connection.
Second, the centrifugal pump installation height Hg calculation
Allowable Suction Vacuum Height Hs refers to the maximum allowable vacuum pressure p1 at the pump inlet.
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) Convey water, but the operating conditions and experimental conditions are different, according to the following conversion
Hs1 = Hs + (Ha-10.33) - (HÏ…-0.24)
(2) Transfer other liquids When the conditions of liquid and villain are 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; the second step will be Hs1 Converted into Hs
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 meters
From a safety point of view, the actual installed pump 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) pump installation at 20 ℃ water delivery;
(2) Change the pump installation height to 80 ° C.
Solution: (1) delivery of 20 ℃ water pump installation height
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 water is transported at 80 ℃, the installation height of the pump is 80
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