1. The key installation technology of centrifugal pumps The key to the installation technology of pipeline centrifugal pumps is to determine the installation height of the water pump (ie, the suction range). This height refers to the vertical distance from the water surface to the center line of the water pump impeller, and cannot be confused with the allowable vacuum suction height. The allowable vacuum suction height marked on the product manual or nameplate of the pump refers to the vacuum value on the water inlet cross-section of the pump, which is measured experimentally at 1 standard atmosphere and a water temperature of 20 degrees Celsius. The water flow rate after the suction pipe is matched is not considered. The installation height of the pump should be the allowable vacuum suction height, that is, the value remaining after deducting the head loss of the suction pipe, and should overcome the actual terrain suction height. The installation height of the water pump cannot exceed the calculated value, otherwise the water pump will not be able to pump water. In addition, what affects the calculated value is the resistance loss head of the suction pipe. Therefore, it is advisable to adopt short pipe layout and install as few pipe fittings as possible, such as elbows. , or consider appropriately matching a larger diameter water pipe to reduce the flow rate in the pipe. It should be pointed out that when the elevation and water temperature of the pipeline centrifugal pump installation location are different from the test conditions, such as when the local elevation exceeds 300 meters or the water temperature of the pumped water exceeds 20 degrees Celsius, the calculated values ??should be corrected. That is, the atmospheric pressure at different altitudes and the saturated steam pressure when the water temperature is higher than 20 degrees Celsius. However, when the water temperature is below 20 degrees Celsius, the saturated steam pressure is negligible. From the perspective of pipeline installation technology, the suction pipeline must be tightly sealed and must not leak air or water. Otherwise, the vacuum at the water inlet of the water pump will be destroyed and the water output of the water pump will be reduced. In severe cases, even water cannot be pumped out. Therefore, pipeline interface work must be done well to ensure the construction quality of pipeline connections. two. Calculation of the installation height Hg of the centrifugal pump. The allowable suction vacuum height Hs refers to the maximum vacuum degree that can be achieved by the pressure p1 at the pump inlet. However, the actual allowable vacuum suction height Hs value is not a value calculated based on a formula, but a value determined experimentally by the pump manufacturer, which is attached to the pump sample for users to review. It should be noted that the Hs value given in the pump sample is the value when clean water is used as the working medium, the working condition is 20C, and the pressure is 1. 013X105Pa. When operating conditions and working media are different, conversion is required. (1) Transport clean water, but the operating conditions are different from the experimental conditions. Hs1=Hs (Ha-10.33)-(Hu-0.24) (2) Transport other liquids according to the following formula. When the transported liquid and antisubstance conditions are different from the experimental conditions, a two-step conversion is required: the first step is to calculate Hs1 from the pump sample according to the above formula; the second step is to convert Hs1 into H cavitation allowance Ah according to the following formula For oil pumps, the installation height is calculated based on the NPSH Oh, which is the degree of vacuum allowed for the pump to suck in liquid, which is also the allowable installation height of the pump, in meters. Check the cavitation head Oh from the oil pump sample and measure its value with clean water at 20°C. If other liquids are transported, corrections are also required, and please consult relevant books for details. Suction range = standard atmospheric pressure (10.33m) - cavitation margin - safety amount (0.5m). The vacuum height of the standard atmospheric pressure pipeline is 10.33 meters. For example, if the necessary cavitation margin of the pump is 4.0m, what is the suction range of h? Solution: △h=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 a negative value, it means that the suction position of the pump should be below the liquid level of the storage tank. Example 2-3 It was found from the sample of the centrifugal pump that the allowable vacuum suction height Hs=5.7m. It is known that the total resistance of the suction pipe is 1.5mH20 and the local atmospheric pressure is 9.81X104Pa, so the dynamic pressure head of the liquid in the suction pipe can be ignored. Try to calculate: (1) The installation of the pump when transporting 20°C clean water; (2) The installation height of the pump is changed to 80°C water. Answer: (1) The installation height of the pump when transporting 20C clean water is known: Hs=5.7m. hf0-1=1.5 meters u12/2g≈0 The local atmospheric pressure is 9.81X104Pa, which basically meets 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 transporting 80C water. When transporting 80C water, the installation height cannot be calculated directly using the Hs value in the pump sample. Instead, the Hs timeline should be converted according to the following formula, that is, Hs1=Hs (Ha-10.33)-( HU-0.24)Ha=9. 81X104Pa≈10mH20, the saturated vapor pressure of 80C water is 47. According to the appendix, the pressure is 4 kPa. Hv=47.4 Hg=Hs1-Hf0-1=0. 78-1.5=-0.72 meters. Substitute the Hs1 value into the formula to get the installation height. Hg=Hs1-Hf0-1=0. 78-1.5=-0.72 meters Hg is a negative value, which means the pump should be installed below the water level of the pool, at least 0. 72m below the water level. 3. Centrifugal pump maintenance parts clearance Standard general dimensional tolerance of centrifugal pumps (SHS01013-92) Coupling and shaft matching The axial clearance between the two end faces of H7/js6 coupling 2.0-6.0 Coupling radial runout 0.06 (rigid )0.08 (Elastic ring pin type) 0.08 (Toothed) 0.15 (Spring type) Coupling end face runout 0.04 (rigid) 0.06 (Elastic ring pin type) 0.06 (Toothed) 0.1 (Spring type) Bearing sliding bearing exceeds bearing pressure . 0.02-0.04 Contact area between lower bearing bush and bearing seat, greater than 60 Contact angle between shaft diameter and bearing 60-90 Contact area between shaft diameter and bearing 2-3 points/cm2 Bearing clearance 0.07-0.12 Log 18 -300.08-0.15 log 30-500.10-0.18 log 50-80