The key to the installation technology of the pipeline centrifugal pump is to determine the installation height of the pump (ie suction stroke). This height refers to the vertical distance from the water source to the centerline of the pump impeller. It cannot be confused with the allowable vacuum height.
![Pipeline centrifugal pump]()
First, the key installation technology of pipeline centrifugal pump
The key to the installation technology of the pipeline centrifugal pump is to determine the installation height of the pump (ie suction stroke). This height refers to the vertical distance from the water source to the centerline of the pump impeller. It is not to be confused with the allowable vacuum height. The allowable vacuum height indicated on the pump product specification or on the nameplate refers to the vacuum value on the pump inlet section. It was measured under the test of 1 standard atmospheric pressure and water temperature of 20 degrees Celsius. It does not take into account the flow of water after the suction pipe is fitted. The installation height of the pump should be such that the suction vacuum height is deducted from the suction pipe loss head, and the remaining part of the value must overcome the actual terrain water absorption height. The installation height of the pump should not exceed the calculated value, otherwise the pump will not be able to pump water. In addition, the magnitude of the influence calculation value is the resistance loss head of the water suction pipe. Therefore, it is advisable to use the shortest pipe arrangement and to install accessories such as elbows as little as possible. It is also conceivable to appropriately match the water pipes with a larger diameter to reduce the flow velocity inside the pipe.
When the elevation and water temperature of the installation point of the pipeline centrifugal pump are different from the test conditions, if the local elevation is more than 300 meters or the water temperature of the pumped water exceeds 20 degrees Celsius, the calculated value shall be corrected. That is, the atmospheric pressure at different elevations and the saturated vapor pressure above 20 degrees Celsius. However, when the water temperature is below 20 degrees Celsius, the saturated vapor pressure is negligible.
From the installation technology of the centrifugal pump of the pipeline, the water-absorbing pipeline requires strict sealing, no air leakage, and water leakage, otherwise the vacuum degree at the water inlet of the water pump will be damaged, so that even if the water output of the water pump is seriously reduced, even water cannot be pumped. Therefore, we must conscientiously do the interface work of the pipeline to ensure the construction quality of the pipeline connection.
Second, the installation height of the centrifugal pump Hg calculation
The allowable suction vacuum height Hs refers to the maximum degree of vacuum that can be reached by the pressure p1 at the pump inlet.
The actual allowable 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 the user to check. It should be noted that the Hs value given in the pump sample is the value when the water is used as the working medium, the operating conditions are 20 ° C and the pressure is 1.013 × 105 Pa, and the conversion is required when the operating conditions and working medium are different.
(1) Conveying clean water, but the operating conditions are different from the experimental conditions, and Hs1=Hs+(Ha-10.33)-(Hυ-0.24) can be converted according to the following formula:
(2) Conveying 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 based on the Hs1 detected in the pump sample; the second step is as follows: Hs1 Converted to H?s2 NPSH Δh
For the oil pump to calculate the installation height, the NPSH is calculated by the NPSH, that is, the vacuum that the pump allows to absorb the liquid, that is, the allowable installation height (m) of the pump. The value of the NPSH was measured from the oil pump sample and also measured with 20 ° C water. Correction is also required if other liquids are delivered.
Suction stroke = standard atmospheric pressure (10.33 m) - NPSH - safety (0.5 m)
The standard atmospheric pressure energy pipeline has a vacuum height of 10.33 meters.
For example: a pump must have a NPSH of 4.0 meters, and ask for a suction Δh?
Solution: Δh=10.33-4.0-0.5=5.83 m 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, the pump's suction port position should be below the tank level.
Example 2-3 A centrifugal pump was found from the sample to allow the vacuum height Hs = 5.7 m. It is known that the total resistance of the suction line is 1.5 mH2O, the local atmospheric pressure is 9.81 x 104 Pa, and the dynamic head of the liquid in the suction line is negligible. Trial calculation:
(1) Installation of the pump when conveying water at 20 ° C;
(2) The installation height of the pump when the water is transported at 80 °C.
Solution: (1) The installation height of the pump is known to deliver 20°C clean water: Hs=5.7m
Hf0-1=1.5m
U12/2g≈0
The local atmospheric pressure is 9.81×104Pa, which is basically consistent with the experimental conditions when the pump is shipped, so the installation height of the pump is Hg=5.7-0-1.5=4.2m.
(2) When the 80 °C water is transported when transporting water at 80 °C, the Hs value in the pump sample cannot be directly calculated. The installation height should be converted according to the following formula: Hs1=Hs+(Ha-10.33)- (Hυ-0.24)
It is known that Ha = 9.81 × 104 Pa ≈ 10 mH 2 O, and the saturated vapor pressure of water at 80 ° C was found to be 47.4 kPa by the appendix.
Hv=47.4×103Pa=4.83mH2O
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
A negative Hg value indicates that the centrifugal pump should be installed below the pool level, at least 0.72 m below the liquid level.
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China Hardware Business Network http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
