In the actual use of centrifugal pumps, often due to various reasons, part of the centrifugal pump actual operating conditions deviate from the high efficiency zone, resulting in excessive energy consumption of centrifugal pumps and operating conditions are not ideal. In order to improve this phenomenon, we must make the necessary technological transformation to the centrifugal pump and further improve the operation efficiency of the centrifugal pump under the premise of meeting the water quantity and lift required by the water supply system. The water intake of a water pumping station in a water plant is designed to be 600,000m3 / d and the first phase is 200,000m3 / d. The water intake equipment of the water pumping station is two 44SAP-14 centrifugal water pumps whose nameplate parameters are Q = 9000m3 / h , H = 28.5m, n = 425r / min, η = 88%, the specific speed of 140 r / min, impeller diameter ф = 1110mm. After two pumps run 3000 hours, the pump impeller has more obvious cavitation damage, pump vibration increased, the bearing temperature is not normal. The unsatisfactory performance of the pump is mainly due to the selection of the pump is based on the long-term 600,000 m3 / d, so the selected head is higher than the first required lift head, resulting in pump operating conditions deviate from the high-efficiency zone, low Head, low efficiency and poor cavitation performance of the regional operation. June 6, 2002, the actual operating point of the pump (Q, H) is (11800,18) (Z point in Figure 1), the operating efficiency is only η, = 75% or so. In order to solve the above problem, in July 2002, it was decided to carry out the alteration of the paralegality. Transformation program 1 replacement of the new pump is the most thorough solution. The new pump can be selected 44SAP-25 centrifugal pump, the pump design parameters: Q = 10800m3 / h, H = 20m, n = 425r / min, η = 90%. Although the pump can be used to replace the original pump motor, but because of the high cost of the program, and time-consuming and laborious, inevitably affect the water plant production, it is not used. 2 When the pump head is too high, the cutting impeller diameter is a simple way to adjust the pump performance, reduce pump power consumption. Considering the first phase of the plant's water supply and the matching of the two pumping stations, the pump should be operated at QB = 9700m3 / h and HB = 18m after cutting by the impeller, ie point B in Figure II. Through the point B for cutting parabola H '= K (Q') 2, and the original water pump curve QH intersection at point A. Point A is to meet the cutting law requirements of the corresponding point B conditions: QA = 10900m3 / h, HA = 22.7m. Impeller after cutting, the performance parameters Q, H changes and the wheel diameter D after cutting the following relationship: QB / QA = DB / DA, HB / HA = (DB / DA) 2 where DA is the original impeller diameter, DB The diameter of the impeller after cutting. Substituting A and B into the above formula, DB / DA = 89%, that is, the cutting capacity of the original impeller is 11%, and the critical cutting speed is 14% of the maximum allowable cutting speed of the impeller at the specific rotation speed of 140r / min. In addition, according to the law of cutting, within the cutting limit, the cutting parabola H '= K (Q') 2 is also called the equivalent efficiency line. That is, the corresponding efficiencies at two points A and B on the curve can be regarded as equal. Since the efficiency at point A is 81%, it is in the low efficiency zone of pump characteristic QH curve and the operating efficiency of point B after impeller cutting is also in the low efficiency operation zone. 3 Non-standard impeller method for the transformation of the pump impeller, that is, design and manufacture of non-standard impeller assembly and operation of the original pump to achieve the purpose of effectively changing the pump performance parameters. According to this idea, can over the 44SAP-25-type pump impeller cutting and parameter integration, so that it meets the requirements of 44SAP-14-type pump. At the same time, the specific speed of the original pump is increased from 140 r / min to 250 r / min, so as to achieve the effect of reducing the lift and improving the operation efficiency of the modified pump. In November 2002, according to this plan, one of the pumps was remodeled. After the transformation of 44SAP-14/25-type pump operating point QD = 9700m3 / h, HD = 18m (point D) in the pump operating high efficiency area, operating efficiency of about 88%. 44SAP-14-type pump after non-standard impeller transformation, the pump vibration was significantly reduced during operation, reduce noise, cavitation has been very well improved. The original pump supporting motor running current from the original 65.5A down to 59.5A, so that pumping station power consumption has dropped dramatically. To 200,000 tons of water a day to calculate, save the day after the transformation 9.6 × 200 = 1920 degrees, six months to save electricity up to 350,000 degrees. The results of the non-standard impeller method to transform the centrifugal pump, you can achieve the following results: 1. The rated parameters can be re-determined according to actual needs, the original pump parameters smaller restrictions; 2. After the transformation of the new pump operating parameters can be more in line with production needs , The pump operating efficiency can be properly increased, energy-saving effect after the rebuild significant; 3. Can be targeted to improve some of the specific pump performance.