Abstract In this paper, the cause of malfunction of 125 LCB-350x2 hydroxylamine feed pump during its use was analyzed. Based on this, the improvement was made and good results were obtained. Abstract The type 125LCB-350X2 haym feed pump is often fault during running, the fault causes are analyzed, the corresponding reformation measures are pointed out and the effect is obvious Key words pump fault analysis reformation The material pump is one of the main equipments in HPO caprolactam production process. The running quality is directly related to the continuity and stability of the entire production. I plant expansion in the new increase of hydroxylamine feed pump is developed two-stage centrifugal pump, its model is 125LCB-350X2. The transmission medium for domain machine process fluid, the composition shown in Table. Pump inlet pressure at atmospheric pressure, outlet pressure 4.0Mpa, flow rate of 70-85 m3 / h, medium density of 1219Kg / m3. Pump speed of 2980rpm, the working temperature is 70 ℃, motor power 160KW. Table I-hydroxylamine feed pump feed ion composition (unit: mmol / g) Name H + NH3OH + NO3-PO43-NH4 + value 2.60.042.892.052.3 Its structure is characterized by: In order to reduce the pump size and axial force, two impeller Face-to-face installation; first-stage impeller contact with the pillow block, located on the shaft. The second stage impeller is separated by an intermediate bushing, the bushing and the impeller are sealed with a tetrafluoroethane pad. The high-pressure end bearing is two SKF7309 bearings, which are installed back to back to increase the rigidity, one 6309 bearing is adopted on the low pressure end, Bearings to bear 2, in order to prevent the bearing temperature rise is too high, the bearing box water cooling; high-pressure side of the bearing for the positioning bearings; shaft seal selection of a single spring balance mechanical seal, mechanical seal mounted on the sleeve. Bushing and impeller with the end of the outer circle When the impeller mouth ring, impeller and sleeve with a PTFE gasket seal, cushion and sleeve diagram shown in Figure (2) and Figure (3); seal cushion by a locking force, Two-stage impeller thickness of 10mm outside the lock nut to provide; allowable axial channeling amount of 0.1mm --- 0.2mm. The associated mating clearances are as follows: the clearance between the center bushing and the pump housing is 0.3 mm; the clearance between the two ports of the two-stage impeller is 0.6 mm. When the pump was put into operation in December, 1999, overload jumping and high-pressure end leakage occurred frequently, which affected the stable operation of the system. When the pump was disassembled and found, the low-pressure end bearing cage was damaged and the mouth ring on the middle bushing and the pump casing was worn seriously. High-pressure end pump shaft and sleeve material infiltration traces. Second: the reasons for analysis A: High-pressure side sleeve seal gasket nut locking force is insufficient, the anti-loose structure is not ideal, resulting in easy leakage of materials from the shaft and shaft sleeve When installing the pump to the low-pressure end of the impeller positioning, the low-pressure side of the impeller Tight tight nut in place to ensure high-pressure side of the impeller to ensure that there is no relative amount of axial channeling, so a total of four impeller impeller seal actually low-pressure end of the nut is only sealed one is the low-pressure impeller back cushion, and the other three seals The cushion is only due to the tightness of the high-end locking nut, which results in the lack of locking force. The locking of the nut is achieved by the washer-back washer. We think this anti-loosening structure will not work well under heavy load and high speed. Open and stop once there will be loose, the actual situation is to use this structure once again to stop the lock nut fastening again. Otherwise, there will be leakage after starting. B: The mechanical seal used is discussed in terms of structure. The "O" ring on the back of the moving ring and the auxiliary seal structure of the bushing are easy to leak when the pressure difference is high. Push ring 2 is a planar ring, the auxiliary seal structure in the high pressure difference above disadvantages [1]: First, the "O" ring is easily squeezed into the gap between the sleeve and the moving ring; the second is the spring force by pushing The ring directly acts on the moving ring. When the working pressure fluctuates, the contact point between the "O" ring and the moving ring and the contact point between the "O" ring and the sleeve can not be synchronized when the pushing ring drives the moving ring to compensate the movement Mobile easily lead to leakage. C: low-pressure side of the bearing options for discussion Low-pressure side of the bearing is selected to bear a certain axial force 6309 deep groove ball bearings, 6309 bearings in the shaft elongation due to heat when the inner and outer rings can not be synchronized to move. When the pump is working, the pump shaft temperature of nearly 50 ℃, the pump shaft and the pump casing will be due to axial elongation, due to the pump shaft and the pump housing materials of different choice Both heat-stretching can not be synchronized to the same size , When the difference is greater than the elongation of the bearing axial clearance reserved, it will be subject to the low-pressure side of the resistance of the bearing can not be free to stretch when the bearing pressure on the low end of the bearing exceeds the bearing limit will lead to Low-end bearing cage is bad, the unilateral clearance between the shaft and the middle bushing mouth ring is only 0.15mm, the bearing cage bad lead to the middle bushing and the mouth ring on the pump shell and cause overload pump jumps. When the pump is installed, the axial allowable channeling of the shaft is only 0.1mm - 0.2mm. At present, the axial clearance reserved for domestic pumps is about 0.5mm in this case. Three: Improvement measures A: The high-pressure end of the lock nut thickness from 10mm to 15mm, while the back of the nut has two threaded buckle made of lining nylon pad flange pressed, the nut itself has automatic anti-loose function Nylon and threaded friction to prevent loose). B: Use multi-spring mechanical seal to improve the seal ring structure on the back. Push the ring with a step ring, the back of the ring in the back of the "O" ring plus a thickness of 1mm PTFE flat pad, the PTFE flat pad to prevent the "O" ring is pushed into the moving ring and sleeve In the gap between. Such auxiliary seal structure when the medium pressure fluctuations, because the push ring will promote the moving ring and the "O" ring as a whole move to eliminate the driven ring and the O ring contact point of leakage, reducing Leak points. In order to install the newly elected mechanical seal on the original sleeve made the corresponding changes in the structure. C: The low pressure side of the bearings to NU309 roller bearings. This type of bearing cage, roller and outer ring as a whole, the bearing inner ring as a component. This will ensure that the pump shaft in the axial free to extend. D: The related parameters were changed without affecting the production conditions. The clearance of the impeller was changed from 0.6mm to 0.8mm. The clearance between the middle bush and the volute was changed from 0.3mm to 0.6mm. IV: Conclusion After the above improvements, the pump life cycle has been greatly extended, the longest use of 15 months, effectively promoted the stability of production and reduced the cost of a large number of overhaul. References [1] "LMV high speed light hydrocarbon pump mechanical seal transformation" Li Bao-yan "fluid machinery" 1998/07