The fit tolerance between assembly parts is a very important parameter, which directly affects the performance of vacuum pump. We have analyzed the precision of the parts and the rough bottom that will appear if the parts are not well matched.
For example, there is a 2x-15 type pump, the user responds that the
vacuum degree is always not high, and the pre pumping finds that it operates
normally without air leakage, oil leakage, noise and temperature rise, but the
vacuum degree is only 20 grids (about 8 * 10-2 Torr). Experience has proved that
the vacuum pump oil is too dirty, there is moisture in the oil, the wrong oil is
used, the parts in the cavity are worn, and the fitting clearance between parts
is too large, etc.
When you start to repair, you can change the oil first,
because this method is the most convenient and effective method. Often, the
vacuum of some pumps is not high, and the problem can be solved by changing the
oil. If you don't change the oil, the next step is to change the oil and clean
it. The vacuum degree of the 2x-15 pump is still 20 grids after oil change, so
we decided to take it apart for inspection. After cleaning, we measured the
cavity size of the parts and found that the end clearance is 4-5 threads, which
is partial to the ball. However, considering this kind of clearance, as long as
the oil circuit is adjusted properly, it is often possible to install the
pengyou after blowing through the oil circuit hole, but it is still 20 grids.
When it is disassembled for the second time, check the non perpendicularity (no
more than half wire, i.e. Q 005 mm), and find that it is not good, send the
surface grinder to grind 2-3 wires off the cavity surface, so that the clearance
between the rotary vane and the cavity end cover is less than 2-3 wires, and the
non perpendicularity is qualified. In this way, after the assembly, the problem
is solved, and the vacuum degree reaches 70 grid ((about 1.5 * 10-2 Torr), which
has met the production use.
This example shows that some problems are very
complex, sometimes it is difficult to check out without careful inspection. At
the same time, we can also see how important the fit clearance of pump parts
is.
The above is just a few examples of low vacuum, not including all
abnormal reasons such as air leakage. Of course, the vacuum pump oil is
insufficient, dirty, oil brand does not match, mixed oil, water in the oil, too
thin oil due to friction heat, no proper amount of oil in the pump cavity due to
blocked oil circuit, producing sealing oil film, valve plate damage, oil
circulation in the pump cavity, poor sealing, etc., which will make the vacuum
degree unable to go up. In the valve, exhaust valve: some of the problems listed
before, will also make the vacuum can not be improved. The selection of fit
clearance and dimensional tolerance of parts are the key points in pump repair,
which should be paid more attention to. In addition, some of the diaphragm press
in vacuum pump, due to the large amount of interference, make the pump cavity
deformation, also produce air leakage, so as to reduce the vacuum degree,
improper assembly, end cap screw loose and tight, rotor axis displacement, bad
rotor movement or spring deformation, aerator valve gasket damage or not
tightened and so on
The vacuum degree of mechanical pump is very low. As long
as we find out the corresponding problems and deal with them, we can repair
them. However, it should be noted that it must be judged according to the
specific situation and careful observation during the test. It is not allowed to
act rashly before the situation or cause of disease is clear. In this way, it is
easy to damage the parts, increase the scope of failure, and cause adverse
consequences or even scrap.
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