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18

Dec

How to caculate installation height of centrifugal pump?
Calculation method of installation height Hg of centrifugal pump

The allowable vacuum height Hs refers to the maximum vacuum degree that the pressure p1 at the pump inlet can reach. The actual allowable suction vacuum height Hs is not a value calculated according to the formula, but a value experimentally determined 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 using clean water as the working medium, sthe operating conditions are 20S℃ and the pressure is 1.013 × 105Pa. When the operating conditions and working medium are different, conversion is required.

1. Transport 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 transported liquid and villain are different from the experimental conditions, two-step conversion is required:
The first step will be Hs1 found in the pump sample according to the above formula;
The second step is to convert Hs1 to H? S according to the following formula

3. Centrifugal pump cavitation margin Δh
For oil pumps, the cavitation allowance Δh is used to calculate the installation height, that is, the vacuum degree that the pump allows to suction liquid, that is, the installation height allowed by the pump, in meters. The cavitation allowance Δh was taken from the oil pump sample, and its value was also measured with 20℃ water. If other liquids are to be transported, calibration is also required. Check the relevant books for details.


 
Suction = standard atmospheric pressure (10.33 m)-cavitation margin-safety amount (0.5 m)
The vacuum height of the standard atmospheric pressure pipeline is 10.33 meters.
For example: the necessary cavitation margin of a pump is 4 hydrant pumps. What is suctionΔh?
Solution: Δh = 10.33-4.0-0.5 = 5.83m
From a safety perspective, the actual installation height of the pump should be less than the calculated value. When the calculated Hg is negative, it means that the position of the suction port of the pump should be below the liquid level of the storage tank.

For example: A centrifugal pump finds from the sample that the allowable suction height Hs = 5.7m. It is known that the total resistance of the suction pipe is 1.5mH2O and the local atmospheric pressure is 9.81 × 104Pa. The dynamic pressure head of the liquid in the suction pipe can be ignored.
Test calculation:
1. Installation height of centrifugal pump when transporting 20℃ water;
2. Installation height of centrifugal pump when transporting 80℃ water.

The installation height of the pump when conveying clean water at 20℃
Hs = 5.7m Hf0-1 = 1.5m u12 / 2g 0
Local atmosphere 9.81 × 104Pa, which is basically consistent 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. 

Installation height of the pump when conveying water at 80℃
When conveying water at 80℃, the Hs value in the pump sample cannot be used to calculate the installation height. The Hs value must be converted according to the following formula, that is,
Hs1 = Hs + Ha-10.33-Hυ-0.24
Ha = 9.81 × 104Pa 10mH2O is known, and the saturated vapor pressure of water at 80℃ is 47.4kPa according to 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, which means that the centrifugal pump should be installed below the liquid level of the pool, at least 0.72m below the liquid level.