Study On Lubrication And Seal Of Large Water Pump Guiding Bearings

Water pump station installed capacity in China is over 70,000 MW. The axial-flow pumps and diffuser mixed-flow pumps are in large proportion of them. Especially, large axial-flow pumps, diffuser mixed-flow pumps or tubular pumps are adopted in all pump stations of Eastern Route of South-to-North Water Transfer Project, which is being constructed. The guide bearing is the key part of a large water pump for its grindability. Its failure rate is very high, and its failure is above 50% of pump unit failure. Studying the guide bearing lubrication and seal performance of the large water pump is significant to decreasing bearing friction loss, lowering failure rate, improving the reliability, saving the maintenance and overhaul cost of pump station. Main works in this dissertation are as follows:Structural styles, operation principles and sealing device types of large pump guide bearings were introduced. Aiming at the open question of guide bearings in application, the influencing factors of guide bearing load of large vertical pumps were analyzed from design, manufacture and installation. The probability load theory of the guide bearing was established. Lubricating and sealing characteristics of the guide bearing were researched by the aid of hydrodynamics and tribology. Lubricating oil pressure and quantity of guide bearings were calculated, probable lubricating malfunctions were analyzed, lubricating water quantity and pressure of clean-water-lubricated guide bearings were calculated. The leakage rate formula of mechanical face seals and comb labyrinth seals, and leakage drainage formula of seal leakage draining device were deduced. The leakage rate and leakage drainage rate of typical guide bearings were calculated. At last, the water pump guide bearings were comprehensively compared from materials, installation, inspection, lubrication, seal, and etc. The selection principles of water pump guide bearings and seal devices were put forward.The results show that guide bearing load of large vertical water pump has something to do with inlet passage of pump station, pump unit manufacture and installation quality, structure pattern. In order to guarantee enough lubricating oil pressure of oil-lubricated guide bearings to form circulation, shaft must have certain rotational speed. Spiral groove parameter, oil quantity up through pitot tube and bearing clearance are the main factors that influence lubricating reliability of oil-lubricated guide bearings.In normal conditions,the leakage rate of mechanical face seal is much less than comb labyrinth seal. But if the elastic springs of mechanical face seal pull off, or stationary seat can't fall back after jacking, or wear faces of rotor and stationary seal ring are irregularity, sealing clearance becomes larger, so the bearings are endangered by large water leakage which can't be drained in time.The bearing capacity of oil-lubricated guide bearings is large, but sealing devices are easy to fail. In contrast, the structure of water-lubricated guide bearing is simple, the lubricating conditions are easy guaranteed, without the problem damaged by immersion, but the bearing capacity is small, and resistance to wear is poor.