There are four water ring vacuum pumps installed in a production line, whose function is to draw vacuum for the flat plate filter. If the vacuum pump cannot operate normally, the corresponding filter cannot work. Since the company has been put into operation for half a year, the vacuum pump has been frequently overhauled due to the leakage of the mechanical seal, and the new mechanical seal has been damaged due to the difficulty of turning in the process of overhauling. Our factory has organized forces to overhauling the vacuum pump for many times, the main content of which is to replace the mechanical seal and deal with the problem of turning difficulty. However, after the replacement of the mechanical seal, the problem of turning difficulty has not been solved Six sets of mechanical seals are wasted, which not only affects the maintenance progress and quality, increases the maintenance cost, but also affects the production.
In order to solve the existing problems of the water ring vacuum pump, the disassembly and maintenance of the water ring vacuum pump was reorganized. Through the inspection and diagnosis of the equipment, the main causes of the failure were analyzed, and effective measures were taken to solve the problem. The following is an analysis and summary of the maintenance of the water ring vacuum pump.
Failure analysis of water ring vacuum pump
Leakage cause of water ring vacuum pump mechanical seal
Improper assembly of mechanical seal
When replacing the non power end mechanical seal, it was found that the seal O-ring on the moving ring was 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.
The pressure of the seal cooling water is too high
The binding force of the sealing surface of the dynamic and static ring of the mechanical seal is exerted by the spring on the dynamic ring. 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. It is preliminarily determined that the water pressure is too high. It is recommended to start the motor after the motor is repaired and use it to further track and find out the real cause of the leakage.
The sealing surface of dynamic and static rings is broken
This is the main reason for the leakage of the machine seal of the water ring vacuum pump.
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 swing
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. The inner ring of bearing is not installed in place
If the inner ring of bearing is not installed in place, the problem described in 1) above will also occur, because the inner and outer rings are displaced in front and back relative to the axial direction, causing one of the two inner rings and the outer ring to be 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 impeller and two end faces of pump is not adjusted properly
The clearance between the impeller and the two end faces 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 mechanical seal is broken, they are stuck with each other.
Correct disassembly and assembly procedures for replacement of machine seal of water ring vacuum pump
1. Remove the cooling water pipe of mechanical seal at both ends of vacuum pump;
2. Remove the power end pulley (this step is not available when replacing the non power end mechanical seal);
3. Remove and hang the mechanical seal at the power end and non power end on the shaft, and pay attention to the light removal and handling; this step is particularly important to avoid damaging the mechanical seal at the intact end. (Note: if the bearings at both ends are overhauled separately, this step is also necessary);
4. Remove the bearing gland at the sealing end of the machine to be replaced, and remove the back cap of the bearing lock;
5. Use jackscrew to push out and remove the bearing seat and bearing together. (at this time, hoist the shaft from the disassembly end to facilitate the bearing ejection);
6. Remove the old mechanical seal from the shaft;
7. Carefully sleeve the new mechanical seal after inspection on the shaft;
8. Clean and check whether the bearing is in good condition and whether the bearing clearance is appropriate;
9. Install the bearing and bearing seat back on the shaft, add lubricating grease to the bearing, tighten the inner ring and lock the back cap, and install the bearing gland (this step also requires the coordination of hoist shaft lifting);
10. Try turning to see if it is easy. Pay special attention not to damage the machine seal during turning;
11. Reassemble the mechanical seals at both ends from the shaft to the seal box;
12. Reassemble the belt pulley (this step is not available when repairing the non power end);
13. Reassemble the condensate pipe, connect the condensate water, and then conduct the turning test for leakage;
14. After the maintenance, the site shall be cleared after the completion of the work.