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.

一、焊死泵体出口自冲洗管

1、 Welding dead pump body outlet self flushing pipe

真空泵的冲洗管一般采用正冲洗，即利用密封介质本身由泵入口通过冲洗管引入密封腔冲洗密封端面，目的是带走机械密封摩擦副产生的热量，降低密封端面温度，防止杂质和固体颗粒沉积及气体滞留等。因冲洗管两端接头密封垫和螺纹配合处容易泄漏，有时冲洗液还有冲蚀波纹管密封的现象，维修时就直接去掉冲洗管，把两端接头处用电焊焊死。没有了冲洗管，冲洗液中断，介质中的杂质和颗粒聚集并粘结在密封腔周围，摩擦副运行工况逐渐变得复杂，最终导致摩擦副温度升高，缩短了机械密封的使用寿命。

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.

二、去掉波纹管密封导水套

2、 Remove the bellows seal water guide sleeve

波纹管式机械密封一般都带有导水套，冷却水自压盖正上方或斜上方进入导水套外侧，经折流后进入导水套和轴套的空腔，经过摩擦副后，再从密封压盖正下方流出。冷却水既起到冷却摩擦副的作用，又能防止密封腔内液体泄漏。因为波纹管与轴套问隙比较小，冷却水中杂质和形成的水垢容易在波纹管里侧表面上聚集，严重时还有可能造成冷却水路堵塞。为减少疏通冷却水路而带来的麻烦，真空泵维修人员往往图省事，随意去掉导水套，结果就造成冷却水未经过折流直接流出密封压盖，使摩擦副表面冷却效果变差，从而导致水温过高而使结垢严重，严重时波纹管密封被卡死，引起密封失效。

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.

三、找正时调整泵轴承托架螺栓

3、 Adjust the pump bearing bracket bolt when aligning

在维修离心泵时，按照零部件的装配顺序，把转子、泵盖、轴承托架等组成的组合件装入泵壳，依靠泵壳与泵盖的止口配合，保证叶轮口环与泵体口环的同轴度，用泵壳与泵盖之问的垫片调整叶轮的轴向位置，调整好同轴度、叶轮轴向位置后，用螺栓将泵壳与泵盖紧固在一起，然后再用螺栓将泵盖与轴承托架紧固在一起，最后装联轴器并找正。找正时应调整电机，先调整轴向问隙，使两半联轴器平行，然后调整径向问隙，使两半联轴器同轴。有些真空泵维修人员在调整电机不能达到要求的情况下，往往采用调整泵盖与轴承托架的紧固螺栓松紧程度来找正，这样做的后果是，因螺栓的紧固程度不同，电机往往产生噪声及振动，严重时，造成整台泵损坏。

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.

四、压缩量大比压缩量小密封效果好

4、 Large compression is better than small compression

在安装机械密封时，不少真空泵维修人员往往从主观上认为压缩量大就比压缩量小密封效果好，但事实上并不是这样。机械密封压缩量过大，造成端面比压过大，导致摩擦副温度升高，密封端面液膜薪度降低、汽化、破坏，甚至密封端面磨损、变形，机械密封弹性元件失去弹性，最终导致密封失效。但机械密封压缩量也不能过小，压缩量过小时，介质压力波动或者停泵后，容易导致密封泄漏。实际维修中，机械密封的压缩量要以机械密封使用说明书上给定的数值为准。

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.

五、立即维修总比不维修效果好

5、 It is better to repair immediately than not to repair

机械密封在使用过程中一旦出现泄漏，不少真空泵维修人员往往认为应该马上维修，事实上某些情况下立即维修效果不一定最好。机械密封运行过程中，尽管出现了某些异常，实际上并没有损坏，可能是介质相关参数变化，密封面之间进入杂质，冷却效果差等情况。经过一段时问运行，介质相关参数正常了，进入密封面的杂质冲走了，应力变形消除了，泄漏量还会明显下降甚至消除。真空泵维修人员在遇到机械密封状态异常时，在条件允许的情况下，一定要认真观察，仔细分析，然后再采取有效措施。这样既避免了更换机械密封的浪费，又可以验证自己对设备故障分析判断的能力，不断积累真空泵维修实践经验，从而使维修技能逐渐提高。

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.