Study On Reliability Of Large Tubular Pump Units

Large tubular pump units are likely to breaking down in terms of the mechanical assembly units, electrical parts and hydraulic components etc., such as the invalidation of blade adjusting mechanism, the breakdown of motor insulation and the bearing failure. These malfunctions influence the reliability of tubular pump units. Therefore, it is significant to researching and improving the reliability of tubular pump key components. The reliability of large bulb tubular pump units was investigated, supported by National Science and Technology Major Project of China in the Eleventh Five-year Plan, Author Special Foundation of National Excellent Doctoral Dissertation of China and so on.The tubular pump unit is a complex system, and its reliability is determined mainly by the reliability of key parts. The structure form, the supporting mechanical characteristics and hydraulic characteristics of tubular pump units were anal ysed. The design principles of tubular pump unit supports were put forward. The judgment standards of key component failures were studied and identified. The NPSH of the impeller import were calculated, the easy cavitation parts of pump blads were judged, and the cavitation life of the most easily cavitation parts based on reliability were worked out, considering the roughness of blade surface, the anti cavitation intensity of the blade material, and pump unit annual running time. The enclosed gear wear fuzzy reliability was calculated. The different bearings’characteristics were compared, and the reliabilities of a single bearing and bearing system were calculated by using exponential distribution failure density function. The operation duty adjusting modes of pump units were compared comprehensively from the aspects of the pump unit starting and stopping characteristics, reliability, manageability, economic operation, etc. According to the fault tree method, the failure probability of hydraulic blade regulating mechanism was calculated, and the life of the regulating mechanism based on reliability was solved.The installation and maintenance procedures of key parts and the structures of pump units are main factors influencing the maintainability of tubular pump units. The malfunctions of the tubular pump units,which operating5000hours annually, were analysed, and the corresponding maintenance time were calculated. When the maintenance degrees of pump units were95%, the verhaul time range of15different kinds of tubular pump units is148.67h～203.23h. The advantages and disadvantages of the maintainability of tubular pump units were evaluated. For the tubular pump unit in the paper, the reliability is90.35%when operating for3.25years, and the reliability of the bearing system is91.04%. After repairing the bearings, the reliability of pump units is increased to99.24%. The reliability of the pump unit, which continued operating3.25years, would be89.7%, and the reliabilities of bearing system, blade adjusting mechanism, gear box, blades and motor respectively are91.04%,98.59%,99.92%,100%and100%. After repairing the bearing systerms for the second time, the reliability of pump units is increased to98.52%. Continueing operating1.5years, the reliability of the pump unit is reduced to90.35%, and the impeller reliability would be decreased rapidly in the9th operation year, so it is necessary to repaire impeller during the8th operation year. The pump unit reliability is increased to98.29%after repairing the gear box, blads and the bearing system.In order to improve the availability of tubular pump units, the measures improving the reliability of the motor and gearbox, the choosing principles and methods of pump unit transmission modes, guide bearings and thrust bearings,and operation duty adjusting modes, were put forward. Since the bearing is easy to failure, its inherent reliability should be raised, or its structure is easy to dismantling, installation and maintenance. The install elevation of the guide bearing is determined to ensure the uniform motor air-gap and pumps leaves gap, and the installation elements of each parts was controlled strictly to improve the installation quality of the pump unit.