The tolerance of the fit between the parts inside the assembly chamber is a very important parameter that directly affects the performance of the vacuum pump. As already analyzed before, the precision of the parts and the rough bottom that will appear if they are not well matched.

　　For example, the user of 2x-15 pump answered that the vacuum level is always not high. Pre-pumping found normal operation, no air leakage, oil leakage, obvious noise, temperature rise, but the vacuum level is only 20 cells (about 8*10-2 torr). Experience proves that the vacuum pump oil is too dirty, there is water in the oil, improper use of oil, the parts in the cavity are worn, and the clearance between the parts is too large.

　　You can replace the oil first, because this method is a convenient and effective one. The vacuum level of some pumps is usually not high, which can be solved by replacing the oil. If the oil is not changed, it will also need to be replaced and cleaned for the next step of partial or complete disassembly and repair. After the oil change, the vacuum level of the 2x-15 pump was still 20 cells, so it was decided to disassemble and check. After cleaning, the cavity size of the parts was measured and the end gap was found to be 4-5 lines and eccentric. However, considering this clearance, usually just adjusting the oil line would be enough, so Pengyou was installed after blowing through the oil line hole, but it was still 20 cells. After the 2nd disassembly, check the non-vertical degree (no more than half a wire, i.e. Q 005 mm). If bad is found, use surface grinder to grind off 2-3 lines from the surface of the cavity so that the clearance between the turntable and the end cover of the cavity fit is less than 2-3 lines and the non-verticality is qualified. In this way, the problem is solved after reassembling and testing the pump. The vacuum level is as high as 70 grams (about 1.5*10-2 torr), which meets the production and use requirements.

　　This example shows that some problems are very complex and sometimes difficult to check without careful inspection. It also shows how important the mating clearance of pump parts is.

　　The above example includes only a few aspects of low vacuum and does not include all abnormal causes, such as air leakage. Of course, insufficient oil for vacuum pump, dirty oil, inconsistent oil grade, oil mixing, water in oil, frictional heat leading to too thin oil, blockage of oil circuit leading to no proper amount of oil in pump cavity, resulting in sealing oil film, damaged valve plate, poor oil circulation in pump cavity, poor sealing, etc., so that the vacuum level does not rise. In the valve plate and exhaust valve: some problems listed above will also make the vacuum degree not improve. When pump repair, the selection of mating clearance and parts size tolerance is key and should be paid high attention. In addition, some intermediate diaphragm presses in vacuum pumps can deform the pump chamber by excessive interference during press-in, which can also lead to leakage, resulting in reduced vacuum, improper assembly, inconsistent tightening of end cap screws, rotor shaft displacement, poor rotation or spring deformation, damaged or untightened mixing valve gaskets, etc.

　　In all cases, the vacuum level of mechanical pumps is very low. We can fix them if we identify the corresponding problems and deal with them. It should be noted, however, that it needs to be judged on a case-by-case basis and carefully observed during the pump test. Do not act recklessly until the situation or the cause is unknown. In this way, it is often easy to damage the parts, expand the scope of the fault, resulting in adverse consequences, or even scrap.