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Pump suction

Date: November 8, 2015 popularity: 141
Description of pump suction range:
Suction range is also called "maximum self-priming height" (also known as "degree of self-priming"). In other words, the maximum height (vertical distance between the pump inlet and the liquid level to be pumped) can be automatically sucked up by the micro pump without water diversion. The suction head is generally reflected in the self-priming pump and centrifugal pump; the suction head of the self-priming pump is larger than that of the centrifugal pump, and the centrifugal pump needs to install the bottom valve to achieve the suction range.
1、 Key installation technology of centrifugal pump
The key to the installation technology of pipeline centrifugal pump is to determine the installation height (i.e. suction head). This height refers to the vertical distance between the water source surface and the center line of the pump impeller. It can not be confused with the allowable vacuum height. The allowable suction vacuum height indicated on the pump product manual or nameplate refers to the vacuum value on the water inlet section of the water pump, and is measured by test under 1 standard atmospheric pressure and water temperature of 20 ℃. It does not take into account the water flow condition after the matching of the suction pipe. The pump installation height should be allowed to absorb the vacuum height, after deducting the loss of suction pipe head, the remaining part of the value, it must overcome the actual terrain suction height. The installation height of water pump should not exceed the calculated value, otherwise, the water pump will not be able to pump water. In addition, the influence of the calculation value is the resistance loss head of the suction pipe. Therefore, the shortest pipeline layout should be adopted, and the fittings such as elbows should be installed as few as possible, and the water pipe with larger diameter can also be considered to reduce the flow velocity in the pipe.
It should be pointed out that when the elevation and water temperature of the installation site of the pipeline centrifugal pump are different from the test conditions, if the local altitude is more than 300 meters or the water temperature being pumped exceeds 20 degrees Celsius, the calculated value should be corrected. That is, the atmospheric pressure at different altitudes and the saturated vapor pressure when the water temperature is higher than 20 ℃. However, when the water temperature is below 20 ℃, the saturated vapor pressure is negligible.
In terms of pipeline installation technology, the water suction pipe is required to have strict sealing, and air and water leakage are not allowed. Otherwise, the vacuum degree at the water inlet of the water pump will be damaged, and the water output of the pump will be reduced, and even the water can not be pumped in serious cases. Therefore, it is necessary to do a good job in pipeline interface work to ensure the construction quality of pipeline connection.
2、 Calculation of installation height Hg of centrifugal pump
The allowable suction vacuum height HS refers to the maximum vacuum degree that can be reached by the pressure P1 at the pump inlet.
However, the actual allowable suction vacuum height HS value is not calculated according to the formula, but is determined by the pump manufacturer through experiments. This value is attached to the pump sample for users to check. When the medium and medium in the pump are converted to 1.05pa, the operating condition should be 1 × 105Pa.
(1) If the operation condition is different from the experimental condition, it can be converted according to the following formula
Hs1=Hs+(Ha-10.33)-(Hυ-0.24)
(2) In the second step, it is not necessary to convert the liquid from HS1 to HS1
Δ 2 h NPSH
For the oil pump, NPSH Δ h is used to calculate the installation height, that is, the vacuum degree of liquid suction allowed by the pump, that is, the allowable installation height of the pump, in meters. The NPSH Δ h was taken from the oil pump sample, and its value was also measured with 20 ℃ clean water. If other liquids are transported, they should also be corrected and checked in detail.
Suction head = standard atmospheric pressure (10.33 m) - NPSH - Safety Quantity (0.5 m) standard atmospheric pressure energy pressure pipeline vacuum height is 10.33 M. For example: the NPSH of a certain pump is 4.0 m, and the suction head Δ H? Solution: Δ H = 10.33-4.0-0.5 = 5.83m
From the safety point of view, the actual installation height of the pump should be less than the calculated value. When the calculated Hg is negative, it means that the suction position of the pump should be below the liquid level of the tank.
Example 2-3 it is found from the sample that the allowable suction height of a centrifugal pump is 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 head of liquid in the suction pipeline can be ignored. Try to calculate:
(1) Installation of pump when transporting 20 ℃ clean water;
(2) The installation height of the pump is changed to 80 ℃ water.
Solution: (1) the installation height of the pump when conveying 20 ℃ clean water
Known: HS = 5.7m
Hf0-1=1.5
mu12/2g≈0
The local atmospheric pressure is 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 = 4.2m.
(2) Installation height of the pump when conveying 80 ℃ water
When conveying 80 ℃ water, the installation height can not be calculated directly by using the HS value in the pump sample. The HS value should be converted according to the following formula, that is
Hs1=Hs+(Ha-10.33)-(Hυ-0.24)
It is known that HA = 9.81 × 104pa ≈ 10mh2o. According to the appendix, the saturated 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
The value of the installation height is obtained by substituting the value of hs172-0.1 into the equation hs1-0.1
If Hg is negative, it means that the pump should be installed below the liquid level of the pool, at least 0.72M lower than the liquid level.

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