Addtime： 2020-07-16 Browse times： 3200
How to quickly and correctly solve the leakage of pipeline or equipment flange is a difficult problem for most engineers. Traditional Chinese medicine pays attention to "watching, hearing and asking for information". In fact, engineers can also judge or solve the gasket leakage problem according to the four steps of "watching, listening, asking and feeling".
"Wang" here mainly refers to the inspection of the gasket used on site (the gasket needs to be cleaned before inspection), whether the gasket is compressed evenly, whether there are marks of misalignment, whether there are cracks, whether there are obvious dimensional deformation and other appearance abnormalities.
For rubber gasket, it is difficult to judge the rubber gasket by this step.
"Asking" is the most important link, and it is also a link that must be understood to solve problems. We need to know the material of gasket, nominal size of gasket, what equipment or pipe gasket is used for, equipment and bolt condition, type and name of medium between flanges, installation procedure, temperature and pressure of gasket, etc., which we need to confirm with gasket users.
The link of "cutting" needs to be assisted by hands-on. The nominal size of the gasket was mentioned in the "question" section, which requires the engineer to actually measure the size of the gasket after use. In order to measure the accuracy, it is better to use micrometer to measure at many points. The thickness, inside and outside diameter or other key dimensions of the gasket need to be measured. After information collection, how to use the above information to analyze and solve problems requires engineers to find key information and analyze and judge according to their own experience.
Usually the first step of judgment is whether the gasket material selected by the customer is suitable for the working condition? In the failure cases we received, there was leakage due to wrong selection.
For example, whether the gasket will be corroded by the medium to be sealed (Fig. 1), whether the medium has strong permeability and the gasket is not dense enough?
How to quickly analyze and judge the leakage of vacuum pump gasket?
Fig. 1 popcorn effect of gasket corroded by monomer medium
In terms of temperature, whether the actual operating temperature on site reaches the limit temperature of the material, whether the gasket should bear the temperature cycle, etc? The gasket of each material also has its own temperature range. For example, the upper temperature limit of rubber gasket is 100 ℃ - 200 ℃, graphite gasket is 454 ℃, non asbestos fiber gasket is 200 ℃ - 300 ℃, PTFE gasket is 260 ℃, and ultra-high temperature material can reach 1000 ℃.
Therefore, when leakage occurs, it is necessary to check whether the gasket actually bears a temperature beyond the temperature range that the material can bear (Fig. 2)?
How to quickly analyze and judge the leakage of vacuum pump gasket?
Figure 2 graphite part of graphite gasket is oxidized at high temperature
In terms of pressure, whether the gasket has withstood the instantaneous pressure impact, and whether the gasket is used on the flange of class 300 or PN40?
How to quickly analyze and judge the leakage of vacuum pump gasket?
Figure 3 leakage of pressed fiber rubber gasket in bubble test
In terms of tightness, is it necessary for fiber gaskets to pass the bubble test (Fig. 3)? Whether the sealing grade of the gasket should reach 1 * 10-5cm3 / s under normal pressure? Similar to this requirement, sometimes some detail in these applications is ignored, and the problem is exposed when the gasket arrives at the site. In fact, these impossible requirements need to be communicated and clarified with customers in time when selecting models, so that customers can re select more suitable products in these special conditions.
Once contacted with a production equipment customer, because the purchased gasket can not pass the bubble test equipment can not be delivered on time. Later, they went to Garlock company. After communication, we found that he used pressed fiber rubber gasket. In terms of material selection, the compressed fiber rubber gasket can not pass the bubble test at all, because the fiber gap of the fiber gasket itself is not dense enough, so it is difficult to pass the air tightness test. Finally, after considering a series of working conditions, we recommend modified polytetrafluoroethylene gylon series products to solve their problems.
When there is no problem in the selection of gasket, it is necessary to use the actual measured gasket size information to analyze the failure reason. For example, the actual compression rate of the gasket can be calculated by using the thickness of the gasket after use combined with the nominal thickness. Through the compression rate, whether the gasket is overpressure or insufficient compressive stress or uneven compression can be determined. Because each type of gasket has a compression range, for example, the compression rate of ordinary rubber gasket is 20% - 45%, the compression rate of non asbestos fiber is 7% - 17%, and the compression rate of modified polytetrafluoroethylene gasket is 7% - 40% (due to the different filling materials and processing methods, the compression rate of expanded tetrafluoroethylene can reach 60% - 80%. If the maximum compression ratio is exceeded, the gasket will be fractured (see Fig. 4);
How to quickly analyze and judge the leakage of vacuum pump gasket?
Fig. 4 gasket collapse due to over compression
If the specified minimum compression rate is not reached, the gasket will not be tightened due to insufficient load (see Fig. 5). Insufficient load or uneven compression of the gasket (see Fig. 6) can easily cause the gasket to blow out under internal pressure, resulting in leakage.
How to quickly analyze and judge the leakage of vacuum pump gasket?
Fig.5 too low compression load causes gasket blow out Fig.6 uneven compression leads to gasket blow out
All of these cases are
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