First, the key technology of centrifugal pump installation Centrifugal pump pipe installation technology is the key to determine the installation of the pump height (ie suction). This height refers to the vertical distance from the water surface of the water source to the center line of the pump impeller. It can not be confused with the allowable vacuum height. The allowable vacuum height indicated on the pump manual or nameplate means the vacuum value on the water inlet section of the water pump, 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 the pipe installation technology, the suction pipe requires strict sealing, can not leak, leakage, otherwise it will undermine the pump inlet of the vacuum, so that the water pump to reduce the amount of water is not pumping even in serious cases. 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 Hs value given in the pump sample is the value of the water used as the working medium, the operating conditions of 20 ° C and the pressure of 1.013 × 105Pa when the operating conditions and working medium are not the same, need to be converted. (1) Conveying clear water, but the operating conditions and experimental conditions are different and can be converted into Hs1 = Hs + (Ha-10.33) - (Hυ-0.24) according to the following formula. When the conditions are different, it needs to be converted into two steps: the first step will be Hs1 detected by the pump sample according to the above formula; the second step will be converted into Hs1 Hs s Hess of levitation margin Δh For the oil pump, when calculating the installation height Calculated with the NPSH Δh, that is, the degree of vacuum that the pump allows to draw 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 can depress the pipeline vacuum height of 10.33 meters. 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) pump installation 20% water delivery; (2) to the delivery of 80 ℃ water pump installation height. Solution: (1) The installation height of the pump when delivering 20 ℃ fresh water is known: Hs = 5.7m Hf0-1 = 1.5mu12 / 2g≈0 The local atmospheric pressure is 9.81 × 104Pa, which basically agrees with the experimental conditions of the pump factory Pump installation height Hg = 5.7-0-1.5 = 4.2 m. (2) Installation height of pump when conveying water at 80 ℃ When installing water at 80 ℃, the installation height can not be directly calculated by using the Hs value in the pump sample. Hs1 = Hs + (Ha-10.33) - (Hυ-0.24) Known Ha = 9.81 × 104Pa≈10mH2O, from the appendix to find the saturated vapor pressure of water at 80 ℃ 47.4kPa. Hv = 47.4 × 103 Pa = 4.83 mH2O Hs1 = 5.7 + 10-10.33-4.83 + 0.24 = 0.78m The value of Hs1 is substituted into the equation to obtain the installation height Hg = Hs1-Hf0-1 = 0.78-1.5 = -0.72m Hg is Negative value, indicating that the pump should be installed below the tank level, at least 0.72m below the liquid level.
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