Addtime： 2020-07-18 Browse times： 1921
Recently, a netizen left a message saying that since the company put into operation for half a year, the vacuum pump was frequently overhauled due to mechanical seal leakage, and the new mechanical seal was damaged due to the difficulty of turning. The company repeatedly organized forces to continue to repair the pump, replace the mechanical seal, and solve the problem of turning difficulty. However, after the replacement of mechanical seal, the problem of turning difficulty has not been overcome, Six sets of mechanical seals were used. How to solve the above problems, the company's employees are very headache?
1、 Fault synthesis of water ring pump
1. Cause of leakage of vacuum pump mechanical seal
1.1. Improper disassembly of mechanical seal
When replacing the mechanical seal of non energy end, it was found that the O-ring on the moving ring was not installed properly. The O-ring should have been installed outside the sealing groove on the moving ring seat. However, the assembly review found that the O-ring was not equipped with such a device, but was wrongly installed outside the tension spring positioning piece, resulting in the deformation of the tension spring, which completely failed to play the role of axial static sealing, resulting in leakage.
1.2. The pressure of icing water in mechanical seal is too high
The adhesion force of mechanical seal dynamic and static ring is imposed by the tension spring on the moving ring. When the frozen water pressure is too high, the water pressure will act on the dynamic and static rings, because the static rings are vivid and immobile, so the water pressure will stimulate the dynamic rings, compress the tension springs to the same position of the static rings, so as to weaken or eliminate the adhesion force of the static and dynamic ring surfaces, resulting in the leakage of the dense book cover. After the maintenance, the mechanical seal at the energy end is filled with ice water for leakage test. The inlet valve is opened 2 / 3 times, and the mechanical seal is complete without leakage. When the water valve is opened more than 2 / 3, the mechanical seal leaks. The three parties (maintenance party, iron oxide motor branch, Sichuan Dayu mechanical seal making factory) preliminarily concluded that the cause was excessive water pressure. It was suggested that the motor should be started up and put into operation after the repair, so as to further track and find out the real cause of the leakage.
1.3. The cover of dynamic and static ring is broken
This is an important cause of the leakage of the mechanical seal of the previous replacement of the pump.
The mechanical seals of energy end and non energy end are disassembled on the same shaft, the impeller is installed beside the shaft, and the bearing support at both ends of the shaft is vivid. When replacing the mechanical seal of energy end or non energy end together, the bearing (bearing pedestal) of corresponding end must be assembled first, and the capacity can be stored in the old mechanical seal, and the new mechanical seal shall be installed. At this time, due to the gravity of the shaft and impeller, the impeller and shaft pipe supported by the bearing at one end will be lost and the shaft will be inclined to the non bearing end. Because the static ring at the end of the pump is not removed with bolts on the pump end cover, and the moving ring is wrapped around the shaft together with the shaft. In addition, because the clearance between the inner ring of the static ring and the shaft is very small, when the shaft is collapsed and tilted, it will cause: a. the absolute displacement of the dynamic and static ring at one end, so that the seal cover of the dynamic and static ring is squeezed against each other, resulting in fragmentation; B. the shaft is indirectly pressed on the stationary ring at the unseparated end On the inner ring, the cover of the static ring is broken or broken.
After understanding and synthesizing the previous replacement operations, the reason why the mechanical seal at one end is replaced well and the mechanical seal at the other end leaks is caused by the above components. In fact, our operators have also thought about a problem, but the steps taken are not right: the previous replacement is to use the bamboo shoots to hang the shaft at the disassembly end to prevent the high and low swing of the shaft. In the theoretical operation, it is proved that this hoisting step has great mistakes, especially not applied to this kind of heavy vacuum pump sealing device. The reason is that it is difficult to master the tension of lifting point and bamboo shoot gourd thoroughly, and it is difficult to prevent the high and low swing of stop shaft.
2. Cause synthesis of vacuum pump turning difficulties
1) The clearance of positioning 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 inner rings and outer rings of double row tapered roller bearings are in contact with conical surfaces, and the inner rings can be taken in from the outer rings. There is a bearing clearance adjusting spacer ring between the two inner rings, that is, the original clearance of the bearing is controlled by the spacer ring between the two inner rings, and the clearance of the normal bearing has been adjusted before delivery.
The bearing is disassembled on the shaft. One of the two rows of inner rings is on the shoulder of the shaft, and the other row is locked on the shaft by the locking back cap. After locking, the two rows of inner rings and spacer rings need not be tightly connected together. With the shaft rotating together, the outer ring and the bearing box are tightly matched. When the thickness of the gap adjusting spacer ring is less than the original thickness, when the back cap is locked, the inner ring and outer ring of the two rows will be squeezed by force, which makes the bearing difficult or helpless to rotate.
2) Bearing inner ring not in place
If the bearing inner ring is not installed in place, the problem mentioned in 1) below will also occur. The reason is that the absolute axial displacement of the inner ring and outer ring causes one of the two rows of inner ring to be pressed against the outer ring. When the energy end bearing was removed, it was found that there was a big eating mark on the shaft surface of the device bearing position. It was concluded that the bearing inner ring was not completely pushed onto the shaft shoulder, which was an important cause of the turning difficulty.
3) The clearance between impeller and pump end face is not 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 seats at both ends. The adjustment step is to add or subtract gaskets between the bearing pedestal and the support positioning surface of the bearing pedestal.
4) Mechanical seal dynamic and static ring seal book cover is broken and stuck each other.
2、 Assembly and disassembly steps of water ring vacuum pump seal replacement error
1. Remove the frozen water pipes at both ends of the pump;
2. Assemble the small copy wheel of the energy end (there is no such step when replacing the mechanical seal of the non energy end);
3. Don't leave the mechanical seal of the energy end and non energy end removed and hung on the shaft, pay attention to the light removal and handle; this step is particularly not a good step, preventing the mechanical seal of the complete end from being damaged. (be careful: then it is necessary to jointly overhaul the bearings at both ends;
4. Remove the bearing gland to replace the machine sealing end, and remove the bearing locking back cap;
5. Remove the bearing block together with the bearing with the jacking screw. (at this time, it is necessary to hang the shaft from the assembly and disassembly end with bamboo shoots, which is inconvenient to eject the bearing);
6. Remove the old mechanical seal from the shaft;
7. Put the new mechanical seal which has been reviewed and completed on the shaft carelessly;
8. Clean and check whether the bearing is complete and whether the bearing clearance is suitable;
9. Install the bearing and bearing seat back on the shaft, add smooth grease to the bearing, tighten the inner ring locking back cap, and install the bearing gland (this step also requires the cooperation of the bamboo shoot hanging shaft);
10. Try the turning gear to see if it's comfortable and leisurely, especially pay attention to the middle and middle parts of the turning gear to damage the mechanical seal;
11. Re install the mechanical seals at both ends from the shaft to the outside of the sealing disc;
12. Refit the small copy wheel (there is no such step when repairing the non energy end);
13. Install the condensate pipe again, and then turn the gear to test the leakage after passing the condensate water;
14. After maintenance, the site shall be cleared.
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