Installation height and suction head selection of centrifugal pump

Installation height and suction head selection of centrifugal pump

I. key installation technology of centrifugal pump

The key of installation technology of pipeline centrifugal pump is to determine the installation height of centrifugal pump, that is, suction head. This height refers to the vertical distance from the water surface of the water source to the centerline of the impeller of the centrifugal pump, which cannot be confused with the allowable suction height. The allowable suction height indicated on the pump product manual or nameplate refers to the vacuum value on the section of the water inlet of the pump, and it is measured by the test under the condition of 1 standard atmospheric pressure and 20 ℃ water temperature. It does not consider the water flow situation after the matching of the suction pipe. The installation height of the water pump should be the rest of the value after the vacuum height is allowed to be absorbed minus the loss head of the suction pipe. It should overcome the actual terrain suction height. The installation height of the water pump shall not exceed the calculated value, otherwise, the centrifugal pump will not be able to pump water. In addition, the influence of the calculated value is the resistance loss head of the suction pipe. Therefore, the shortest pipe layout should be adopted, and the fittings such as elbows should be installed as little as possible, and the pipes with larger diameters should also be considered to reduce the flow velocity in the pipes. 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 elevation is more than 300 meters or the water temperature pumped is more than 20 ℃, the calculation value should be corrected. That is, the atmospheric pressure at different altitudes and the saturated steam pressure at water temperature higher than 20 ℃. However, when the water temperature is below 20 ℃, the saturated steam pressure can be ignored. In terms of pipe installation technology, the water suction pipe shall be strictly sealed, without air leakage or water leakage, otherwise the vacuum degree at the inlet of centrifugal pump will be damaged, the water output of centrifugal pump will be reduced, and even the water will 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.

II. Calculation 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 allow. The actual allowable vacuum height HS value is not calculated according to the formula, but measured 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 with clear water as working medium, operating conditions of 20 ℃ and pressure of 1.013 × 105Pa. When the operating conditions and working medium are different, conversion is required. 1. Transport clear water, but the operating conditions are different from the experimental conditions. The following formula can be used to convert HS1 = HS + ha-10.33-h nu-0.24 2 transport other liquids. When the conditions of the transported liquid and the villain are different from the experimental conditions, two conversion steps are needed: the first step is to convert the HS1 found in the pump sample according to the above formula; the second step is to convert the HS1 into the H? S 2 NPSH Δ h for the oil pump according to the following formula, When calculating the installation height, NPSH Δ h is used to calculate, that is, the vacuum degree of the liquid allowed to be absorbed by the pump, that is, the allowable installation height of the pump, in meters. The NPSH Δ h is checked from the oil pump sample, and its value is also measured with water at 20 ℃. If other liquids are transported, they need to be corrected. Please refer to the relevant books. Suction head = standard atmospheric pressure (10.33m) - NPSH - Safety amount (0.5m) standard atmospheric pressure energy pressure pipeline vacuum height 10.33m. For example: a pump must have a NPSH of 4.0m, and calculate the suction head Δ H? Solution: Δ H = 10.33-4.0-0.5 = 5.83m from the perspective of safety, 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 storage tank. Example 2-3 a centrifugal pump found from the sample that the allowable vacuum height HS = 5.7m. It is known that the total resistance of the suction line is 1.5mh2o, and the local atmospheric pressure is 9.81 × 104pa. The dynamic pressure head of the liquid in the suction line can be ignored. Trial calculation: 1. Installation of centrifugal pump when delivering 20 ℃ clean water. 2. Change the installation height of centrifugal pump when delivering 80 ℃ water. Solution: 1. Installation height of pump when delivering 20 ℃ clean water. It is known that: HS = 5.7m hf0-1 = 1.5m U12 / 2G ≈ 0 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. When 80 ℃ water is delivered, the installation height of the pump cannot be calculated directly by the HS value in the pump sample. It is necessary to convert the HS according to the following formula, i.e. HS1 = HS + ha-10.33-h У - 0.24 it is known that HA = 9.81 × 104pa ≈ 10mh2o, and the saturated steam pressure of 80 ℃ water is 47.4kpa according to the appendix. HV = 47.4 × 103 PA = 4.83 mh2o, HS 1 = 5.7 + 10-10.33-4.83 + 0.24 = 0.78m, substituting the value of HS 1 into the equation, the installation height Hg = HS 1-hf0-1 = 0.78-1.5 = - 0.72M, Hg is a negative value, indicating that the pump should be installed below the water level of the pool, at least 0.72M lower than the water level, single-stage double suction centrifugal pump is a new type of high-efficiency and energy-saving pump, and its operation efficiency can be achieved under the same energy consumption conditions It is nearly 20% higher than the raw water pump. 1. It has compact structure, beautiful appearance, good stability and easy installation. 2. The double suction impeller with smooth operation and optimized design can reduce the axial force to the minimum and has excellent hydraulic performance. After precision casting, the inner surface of the pump casing and the impeller surface have remarkable cavitation resistance and high efficiency. 3. SKF and NSK Bearings are selected to ensure smooth operation, low noise and long service life. 4. The shaft seal shall be Burgmann mechanical seal or packing seal. It can guarantee 8000 hours operation without leakage. 5. The installation form does not need to be adjusted during assembly. It can be used according to the site conditions. branch