Failure analysis of water ring vacuum pump

1 Leakage reason of mechanical seal of vacuum pump 1.1 When the mechanical seal is improperly assembled and replaced with the mechanical seal at the non power end, it is found that the seal O-ring on the moving ring is not installed properly during the disassembly The O-ring should have been installed in the seal groove on the moving ring seat However, it was found during disassembly and inspection that the O-ring was not so installed, but was wrongly installed in the spring locating plate, resulting in the deformation of the spring, completely failing to play the role of axial static seal, resulting in leakage 1.2 When the pressure of the cooling water of the mechanical seal is too high, the bonding force of the sealing surface of the dynamic and static rings of the mechanical seal is exerted by the spring on the dynamic rings When the cooling water pressure is too large, the water pressure will act on the dynamic and static rings Because the static ring is fixed, the water pressure will push the dynamic ring and compress the spring in the opposite direction of the static ring, thus weakening or offsetting the adhesion force of the dynamic and static ring surface, resulting in the leakage of the sealing surface After maintenance, the power end machine seal shall be filled with cooling water for leakage test The water inlet valve shall be opened less than 2 / 3, and the machine seal shall be intact without leakage When the water valve is opened more than 2 / 3, the machine seal shall have leakage The three parties (maintenance party, alumina motor department, Sichuan Dayu machine seal manufacturer) preliminarily determine that it is caused by excessive water pressure It is recommended to start the motor for operation after the motor is repaired, and further track and find out the real cause of the leakage 1.3 The sealing surface of the dynamic and static ring is broken, which is the main reason for the leakage of the previous replacement of the pump seal The power end and non power end machine seal are assembled on the same shaft, the impeller is installed in the middle of the shaft, and the two ends of the shaft are installed with bearing support and fixed When the power end or non power end machine seal is replaced separately, the bearing (bearing seat) at the corresponding end must be disassembled before the old machine seal is taken out and the new machine seal is installed At this time, because of the gravity of the shaft and impeller, the impeller and shaft that lose the bearing support at one end must fall down and the shaft inclines to the bearing free end Because the static ring at the end not removed is fixed on the pump end cover with bolts, while the dynamic ring is fixed on the shaft and rotates with the shaft In addition, because the fit clearance between the inner ring of the static ring and the shaft is very small, when the shaft collapses and inclines, it will cause: a the relative displacement of the dynamic and static ring at the end not removed, which makes the sealing surfaces of the dynamic and static rings squeeze each other illegally, causing fragmentation; B the shaft is directly pressed on the static ring at the end not removed On the inner ring, the sealing surface of the stationary ring is broken or broken Through the understanding and analysis of the previous replacement work, the reasons for the replacement of one end and the leakage of the mechanical seal at the other end are all caused by the above factors In fact, our operators have taken this problem into consideration, but the method adopted is wrong: the previous replacement is to use the hoist to hang the shaft at the disassembly end to prevent the shaft from swinging up, down, left and right The actual operation proves that this hoisting method has a great error, especially is not suitable for the installation of such a large vacuum pump seal The reason is that the tension of lifting point and hoist is difficult to be fully controlled, and it is difficult to avoid the up and down left and right swing of shaft 2 Cause analysis of the difficulty in turning the vacuum pump 1) the clearance between the locating bearings at both ends of the pump was not adjusted properly The bearings at both ends of the pump are double row tapered roller bearings The two rows of inner rings of double row tapered roller bearings are in contact with the outer ring, and the inner ring can be separated from the outer ring There is a bearing clearance adjusting spacer ring between the two inner rings, that is, the original bearing clearance is controlled by the spacer ring between the two inner rings Generally, the clearance of the bearing has been adjusted when it leaves the factory The bearing is assembled on the shaft, one of the two inner rings is on the shoulder of the shaft, and the other is locked on the shaft by the locking back cap After locking, the two inner rings and the spacer ring should be closely connected to rotate with the shaft, and the outer ring and the bearing box are tightly matched If the thickness of the clearance adjusting spacer ring is less than the original thickness, when the back cap is locked, the two inner rings and the outer ring are squeezed by unconventional force, which makes it difficult or impossible for the bearing to rotate 2) if the inner ring of the bearing is not installed in place, the problems described in 1) above will also occur The reason is that the inner and outer rings are misaligned in the axial direction, resulting in one of the two inner rings and the outer ring being squeezed by unconventional force When removing the bearing at the power end, it was found that there was a large scratch on the shaft surface where the bearing was installed It was analyzed and judged that the inner ring of the bearing was not completely pushed on the shaft shoulder, which was the main reason for the difficulty of turning this time 3) the clearance between the impeller and the two end faces of the pump has not been adjusted well The clearance between the impeller and the two end faces of the pump body of the water ring vacuum pump is adjusted by moving the bearing blocks at both ends The adjustment method is to add and subtract gasket between the bearing seat and the positioning surface of the bracket for installing the bearing seat 4) after the sealing surface of the dynamic and static rings of the machine seal is broken, they are stuck with each other.