Key technology for installation of pipeline centrifugal pump: pump installation height is suction selection

First, the key installation technology of 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. The test was carried out under the conditions of 1 standard atmospheric pressure and a 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 the value of the remaining part that allows the suction vacuum height to be deducted from the loss of the suction pipe. It must overcome the actual terrain water absorption height. The pump installation height cannot 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 suction pipe. Therefore, it is advisable to use the short piping arrangement of the Zui, and to install accessories such as elbows as little as possible. It is also conceivable to properly fit the water pipes with a larger diameter to reduce the flow velocity inside the pipe.

It should be pointed out that when the elevation and water temperature of the installation place of the pipeline centrifugal pump are different from the test conditions, such as the local altitude above 300 meters or the water temperature of the pumped water exceeds 20 degrees Celsius, the calculated value should 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 pipeline installation technology, the suction pipe requires strict sealing, and it cannot leak or leak water. Otherwise, the vacuum at the water inlet of the pump will be destroyed, so that the water output of the pump will be reduced, and even if it is serious, the water will not be pumped. Therefore, it is necessary to carefully 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

Allowing the suction vacuum height Hs means that the pressure p1 at the pump inlet can be allowed to reach a large vacuum.
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. When the operating conditions and working medium are different, the conversion is required.

(1) Conveying clean water, but the operating conditions are different from the experimental conditions, and can be converted according to the following formula: Hs1=Hs+(Ha-10.33) - (Hυ-0.24)

(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: * step according to the above formula will be Hs1 detected by the pump sample; second step will be converted according to the following formula: Hs1 Into H?s

2 NPSH Δh

For the oil pump , calculate the installation height with the NPSH Δh, that is, the vacuum that the pump allows to absorb the liquid, that is, the allowable installation height of the pump, in meters. The NPSH Δh was taken from the oil pump sample and its value was also measured with 20 ° C water. If other liquids are transported, corrections are also required. Check the relevant books.

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 to allow the vacuum height Hs = 5.7 m from the sample. 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 20°C clean water;
(2) The installation height of the pump when transporting water 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=4.2 m.

(2) Mounting height of the pump when transporting 80°C water

When transporting water at 80 °C, the installation height cannot be calculated directly from the Hs value in the pump sample. It is necessary to convert the Hs according to the following formula, ie 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=47.4×103 Pa=4.83 mH2O
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
Hg is a negative value, indicating that the pump should be installed below the pool level, at least 0.72m below the liquid level.