Study On Durability Of Large Water Pump Units

In China, the total equipped capacity of pump stations is over 70,000 MW, and there are over 46,000 pump stations, more than 5500 of which are middle or large ones. The repair of pump unit costs much manpower, material and financial resources every year, and it influences the operation of the pump station. The durability of the pump units affects the failure created of pump unit directly. Maintenance cost is increased because of frequent failures and repairs. Therefore, it is significant to improving the reliability of the pump station and saving maintenance cost by studying and improving the durability of the pump unit and determining a reasonable maintenance cycle.The wear of pump guides bearing, the cavitation of pump blades and shells, and the insulation aging of electric motors are main factors influencing the durability of pump unit. They are the key parts of the pump unit. The main factors affecting the durability of key parts were analyzed. Combining pumping operation condition, the formulas of the end face seal wearing speed, the water-lubricating guiding bearing wearing speed, pump blades and pump shells cavitation erosion speed, and the motor insulation aging speed were founded by existing research results and experimental data. Considering uncertainty of some main factors, the theory was created, which was used to calculate servicing life based on reliability of the key parts influenced by much factors. Calculation method was presented. Aiming at different patterns and operating conditions, the influence of related factors on key parts was analyzed, and the methods to improve the durability of pump unit were presented. At last, with the key parts servicing life, the pump unit servicing life on different reliability level was calculated and the heavy repair period was determined with the goal that annual average cost and direct economy lose of failure repaired was minimum.The results show that: the pressure on the sealing face of the oil--lubricating guiding bearing is the sum of the weight of seal stationary ring and stationary seat, the spring pressure, and the hydraulic thrust, and among them the proportion of hydraulic thrust is small. The main factors that affecting the wearing speed of water-lubricating guiding bearing are the radial load of guiding bearing, the sediment concentration of lubricating water, and the wear strength of bearing bush. With the same working condition, the life of rubber guiding bearing lubricated with clear water is about 8 times of the one lubricated with river water. The anti-cavitatiom strength of the pump, the operation condition of the pump, and the sediment concentration of the pumped water are the main factors that influence the pump blade cavitation speed, and among them the inundation depth of impeller and the value pump operation lift deviates from the design lift have biggish influence. The impeller shell cavitation speed is affected by the anti-cavitation strength of its material and the impeller clearance .The insulation aging speed of pump mating electric machine is affected by the insulation material and the working condition of the electric machine. In the same working condition, the aging speed of mylar insulation is about 1.7 times of the epoxy insulation.The life of the key components is different from each other widely. For the pump station in the paper, the life having 95% confidence of the insulation of the mating electric machine, the pump blade, the pump impeller housing, and the mechanical seal are respectively 28.6, 8.2, 5.7 and 3.4 years. When the heavy repair period of the pump station is 5.3 years, the annual expense of repair cost and economic losses is least, and the pump unit has 98% confidence before heavy repair.