Addtime： 2020-07-17 Browse times： 3206
There are a lot of matters needing attention in the maintenance of vacuum pump, and there are also some common sense mistakes, which are most likely to happen to non professional vacuum pump maintenance personnel. The following five common sense mistakes should be avoided in vacuum pump maintenance.
1、 Welding dead pump body outlet self flushing pipe
The flushing pipe of vacuum pump generally adopts positive flushing, that is, the sealing medium itself is introduced into the seal cavity through the flushing pipe from the pump inlet to wash the seal end face. The purpose is to take away the heat generated by the friction pair of the mechanical seal, reduce the temperature of the seal end face, and prevent the deposition of impurities and solid particles and gas retention. Because the sealing gasket and thread fitting of the two ends of the flushing pipe are easy to leak, and sometimes the flushing fluid can erode the seal of the bellows, the flushing pipe is directly removed during maintenance, and the joints at both ends are welded by electric welding. Without the flushing pipe, the flushing fluid is interrupted, the impurities and particles in the medium gather and bond around the sealing cavity, and the operation conditions of the friction pair gradually become complex, which eventually leads to the temperature rise of the friction pair and shortens the service life of the mechanical seal.
2、 Remove the bellows seal water guide sleeve
Generally, bellows type mechanical seal is equipped with water guide sleeve. The cooling water enters the outer side of the water guide sleeve from the top or inclined top of the gland, enters the cavity of the water guide sleeve and shaft sleeve after folding, and flows out from the bottom of the sealing gland after passing through the friction pair. The cooling water can not only cool the friction pair, but also prevent the leakage of liquid in the sealing cavity. Because the gap between the bellows and the shaft sleeve is relatively small, the impurities and scale in the cooling water are easy to gather on the inner surface of the bellows, and in serious cases, the cooling water path may be blocked. In order to reduce the trouble caused by dredging the cooling water path, the vacuum pump maintenance personnel often try to save time and remove the water guide sleeve at will. As a result, the cooling water directly flows out of the sealing gland without the baffle flow, which makes the surface cooling effect of the friction pair worse, resulting in excessive water temperature and serious scaling. In serious cases, the bellows seal is stuck, resulting in seal failure.
3、 Adjust the pump bearing bracket bolt when aligning
During the maintenance of centrifugal pump, the assembly composed of rotor, pump cover and bearing bracket is installed into the pump shell according to the assembly sequence of parts. The coaxiality of impeller mouth ring and pump body mouth ring is ensured by the stop fit of pump shell and pump cover. The axial position of impeller is adjusted by the gasket between pump shell and pump cover. After the coaxiality and impeller axial position are adjusted, the pump shell and pump cover are connected by bolts Fasten them together, then fasten the pump cover and bearing bracket with bolts, and finally install the coupling and align it. The motor should be adjusted when the alignment is correct. The axial gap is adjusted first, so that the two halves of the coupling are parallel, and then the radial gap is adjusted to make the two shaft coupling coaxial. Some vacuum pump maintenance personnel often adjust the tightness of the fastening bolts of the pump cover and bearing bracket to find the alignment when the motor cannot meet the requirements. The consequence of this is that the motor often produces noise and vibration due to the different tightening degree of the bolts, and in serious cases, the whole pump is damaged.
4、 Large compression is better than small compression
In the installation of mechanical seals, many vacuum pump maintenance personnel tend to subjectively think that a large amount of compression is better than a small amount of compression, and the sealing effect is better, but in fact it is not the case. Excessive compression of mechanical seal results in excessive specific pressure at the end face, which leads to the increase of friction pair temperature, the decrease of liquid film thickness, vaporization and damage of seal face, even wear and deformation of seal face, and the elastic element of mechanical seal loses elasticity, which eventually leads to seal failure. However, the compression capacity of mechanical seal should not be too small. If the compression amount is too small, the medium pressure fluctuation or pump stop will easily lead to seal leakage. In actual maintenance, the compression amount of mechanical seal shall be subject to the value given in the operation manual of mechanical seal.
5、 It is better to repair immediately than not to repair
Once mechanical seal leakage occurs in the process of use, many vacuum pump maintenance personnel often think that it should be repaired immediately. In fact, in some cases, the immediate repair effect is not necessarily the best. In the process of mechanical seal operation, although there are some abnormalities, it is not damaged in fact. It may be due to the change of medium related parameters, impurities entering between sealing surfaces, poor cooling effect, etc. After a period of operation, the relevant parameters of the medium are normal, the impurities entering the sealing surface are washed away, the stress and deformation are eliminated, and the leakage rate will obviously decrease or even eliminate. When the vacuum pump maintenance personnel encounter the abnormal state of mechanical seal, they must observe and analyze carefully when conditions permit, and then take effective measures. This not only avoids the waste of replacing the mechanical seal, but also can verify the ability to analyze and judge the equipment fault, and continuously accumulate the practical experience of vacuum pump maintenance, so as to gradually improve the maintenance skills.
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