Sealing gasket is to prevent leakage, specifically to prevent the leakage of liquid or gas through the gasket sealing connection. For pump gasket seal, the main sealed medium is generally liquid, gas or dust. Then the leakage of gasket seal is mainly affected by the following two situations: first, there are gaps on the sealing surface. Second, there is a pressure difference between the two sides of the sealing part. Gasket sealing needs to solve the problem of eliminating or reducing the gap between sealing surfaces. The clearance includes the clearance between the sealing surfaces and the internal clearance of the sealing device. The main reasons for leakage of gasket failure are as follows.

1.Effect of Compressive Stress on Gaskets

In order to achieve the sealing effect, it is necessary to apply enough pressure on the gasket to make it elastic or plastic deformation, so as to fill the bump of the sealing surface. However, when assembling, the compression force required by the gasket can not be reached, or the compression bolt is loosened by mechanical vibration in long-term operation. In addition, the aging deformation of the gasket material and the loss of the original elasticity will cause the gasket to fail and leak. If the compression stress of gasket is too large, it is particularly easy to crush the gasket, thus losing the resilience ability, unable to compensate for the flange surface separation caused by temperature and pressure, resulting in a sharp increase in leakage rate. Therefore, in order to maintain a good seal, the gasket compression stress must be kept within a certain range.

2. Paperboard with cracks or wrinkles and uneven internal structure or thickness of gasket material makes the gasket itself form a gap. When the elastic deformation produced by gasket is insufficient to fully fill the gap, leakage is inevitable.

3. Working Conditions of Gasket Seals

Under different pressure and temperature, the leakage rate is different. The pressure difference between the two sides of the sealing surface is the main driving force for leakage. The greater the pressure difference, the easier the medium will overcome the resistance of the leakage passage and the easier the leakage will be. Temperature has a great influence on the sealing performance of the connection structure. The results show that the elastic and plastic deformation of gasket increases with the increase of temperature, while the resilience decreases with the increase of temperature, and the creep increases with the increase of temperature. With the increase of temperature, the aging, weightlessness, creep and relaxation of gaskets will become more and more serious. In addition, temperature also has a great influence on the viscosity of the medium. With the increase of temperature, the viscosity of the liquid decreases, while the viscosity of the gas increases. The higher the temperature, the easier the leakage will occur.

4. Material of gasket does not match the medium it conveys.

Because of the diversity of chemical properties of chemical products transported by pumps, and the addition of a few additives to the fuel to increase the combustion value or to change the products after combustion, some properties of the fuel will change. Therefore, it is not easy to select the gasket material suitable for the medium of transportation, and therefore it is often used. Leakage occurs when gaskets are eroded due to incompatibility.

5. The influence of gasket material size

A. The influence of gasket thickness: Under the same compression load and the same medium pressure, the leakage rate decreases with the increase of gasket thickness. This is because under the same axial load, the thick gasket has a larger compression rebound. When the initial sealing conditions have been achieved, the thick gasket with larger elastic reserves can compensate for the relative separation between the sealing surfaces caused by the medium pressure better than the thin gasket, and make the gasket surface retain a larger residual compression stress. Force, thus reducing the leakage rate. Because of the influence of friction on the end face, the surface of the gasket is in a stress state of three-dimensional compression, and the deformation resistance of the material is larger; while in the middle of the gasket, the influence of the end is smaller, and the deformation resistance is smaller. Under the same preload, the plastic deformation of the middle part of the gasket is easier than that of the surface of the gasket. At this time, it is more difficult to establish the initial seal. Therefore, when the thickness of the gasket reaches a certain value, the sealing performance does not change or even deteriorate. In addition, the thicker the gasket, the larger the leakage area and the larger the leakage rate.

B. The influence of gasket width: Within a certain range, with the increase of gasket width, the leakage rate decreases linearly. This is because the leakage resistance of the medium is proportional to the length of the leakage passage (proportional to the width of the gasket) in the effective width of the gasket. But it can not be said that the wider the gasket, the better, because the wider the gasket, the larger the surface area of the gasket, so to produce the same compressive stress on the gasket, the bolt force of the wide gasket will be much greater through the narrow gasket.

Leakage is essentially a kind of medium flow in space, that is, from limited space to infinite space, or from internal to external, and vice versa. The reason of the medium flowing between the two is the power source of the leakage. The leakage usually occurs at the two ends of the interface. There are two conditions for the leakage: one is the cross-section area at the junction, the other is the pressure difference or concentration difference between the two ends.

First of all, any equipment or machinery processing will have more or less accuracy problems, there will inevitably be gaps on the sealing surface, it is difficult to achieve complete fit, especially when the hardness of the contact surface between the two is high, there is no plastic deformation, such as the connection of flange joints, and the advantages of media, especially gas and liquid, are non-porous. No. So leakage will inevitably occur.

The causes of leakage caused by sealing gasket failure and the measures to avoid it: if we know the causes of leakage, we should start with two aspects to solve this problem: one is how to reduce the leakage cross-section area, the other is how to reduce the power of leakage. Increase overall resistance to flow.

The best way here is to use sealing gaskets, because after applying enough pre-tightening force on the sealing surface, the sealing gaskets can undergo plastic deformation. When the stress increases enough to cause obvious plastic deformation on the surface, the gap between the sealing surfaces can be filled and the leakage passage can be blocked.

The purpose of using gaskets is to make use of the plastic deformation characteristics of gaskets under the action of compressive load, so as to make them fill the small bumps of flange sealing surface, thus achieving sealing.