Sealing gasket is to prevent leakage, specifically to prevent liquid or gas from leaking out through the gasket sealing connection. For pump gasket sealing, the main sealed medium is generally liquid, gas or dust. So the main manifestations that affect gasket sealing leakage are the following two situations: one is that there is a gap on the sealing surface. Secondly, there is a pressure difference on both sides of the sealed area. The problem of gasket sealing is to eliminate or reduce the gap between the sealing surfaces. This type of gap includes gaps between sealing surfaces and gaps within the sealing device itself. The main reasons for leakage caused by gasket failure are as follows.

1. The influence of compressive stress on the gasket

In order to achieve a sealing effect, it is necessary to apply sufficient pressure to the sealing gasket, which can cause it to undergo elastic or plastic deformation, thereby filling the unevenness of the sealing surface. However, during assembly, if the required clamping force for the gasket cannot be achieved, or if the mechanical vibration during long-term operation causes the clamping bolt to loosen, and if the gasket material ages and deforms, losing its original elasticity, it will cause the gasket to fail and leak. If the compression stress of the gasket is too high, it is particularly easy to crush the gasket and lose its rebound ability, which cannot compensate for the separation of the flange surface caused by temperature and pressure, resulting in a sharp increase in leakage rate. Therefore, to maintain a good seal, it is necessary to keep the compression stress of the gasket within a certain range.

2. The uneven internal structure or thickness of the gasket material with cracks or wrinkles in the cardboard creates gaps in the gasket itself. When the force acting on the gasket is insufficient to fully fill these gaps, leakage is inevitable.

3. Working conditions for gasket sealing

The leakage rate varies under different pressures and temperatures. The pressure difference on both sides of the sealing surface is the main driving force for leakage. The larger the pressure difference, the easier it is for the medium to overcome the resistance of the leakage channel, making leakage easier. Temperature has a significant impact on the sealing performance of the connecting structure. Research has shown that the elastic and plastic deformation of the gasket increases with increasing temperature, while the rebound performance decreases and the creep amount increases with increasing temperature. And as the temperature increases, the aging, weight loss, creep, and relaxation phenomena of the gasket will become increasingly severe. In addition, temperature also has a significant impact on the viscosity of the medium. As the temperature increases, the viscosity of the liquid decreases while the viscosity of the gas increases. The higher the temperature, the more likely leakage occurs.

4. The material of the gasket is not compatible with the medium being conveyed

Due to the diversity of chemical properties of the chemical products transported by the pump, as well as the addition of small amounts of additives to the fuel to increase its combustion value or change its combustion products, some properties of the fuel may change. Therefore, it is not easy to choose gasket materials that are suitable for the conveying medium, and leakage often occurs due to gasket erosion caused by incompatibility.

5. The influence of gasket material size

a. The influence of gasket thickness: Under the same compression load and medium pressure, the leakage rate decreases with the increase of gasket thickness. This is because under the same axial load, thick gaskets have a larger compression rebound. In the case where the initial sealing conditions have been reached, thick gaskets with a larger elastic reserve can better compensate for the relative separation between sealing surfaces caused by medium pressure than thin gaskets, and retain a larger residual compression stress on the gasket surface, thereby reducing the leakage rate. The conditions for establishing an initial seal vary depending on the thickness of the gasket. Due to the influence of frictional forces on the end face, the gasket surface exhibits a three-dimensional compressive stress state, resulting in greater deformation resistance of the material; The middle part of the gasket is less affected by the end, and its deformation resistance is also smaller. Under the same preload, plastic deformation is more likely to occur in the middle of the gasket than on the surface of the gasket, making it more difficult to establish an initial seal. Therefore, when the thickness of the gasket reaches a certain value, the sealing performance does not change or even deteriorates. In addition, the thicker the gasket, the larger the area of permeation leakage, and the higher the permeation leakage rate.

b. The influence of gasket width: Within a certain range, as the gasket width increases, the leakage rate decreases linearly. This is because the medium leakage resistance within the effective width of the gasket is proportional to the length of the leakage channel (proportional to the width of the gasket). But it cannot be said that the wider the gasket, the better, because the wider the gasket, the larger the surface area of the gasket. This will generate the same compressive stress on the gasket, and the bolt force of the wide gasket will be much greater than that of the narrow gasket.

Leakage is essentially a flow of medium in space, that is, from finite space to infinite space, or from the inside to the outside, and vice versa. The reason for the flow of the medium between the two is the power source of leakage, which usually occurs at both ends of the interface. There are two conditions for leakage: first, there is a cross-sectional area available for leakage at the interface, and second, there is a certain pressure or concentration difference at both ends.

Firstly, any equipment or mechanical processing will inevitably have some degree of accuracy issues, and gaps will inevitably appear on the sealing surface, making it difficult to achieve a complete fit, especially when the contact surface between the two is hard and there is no plastic deformation, such as the connection of flange joints, and the medium, especially gas and liquid, has the advantage of penetrating everywhere. So leakage is inevitable.

The reasons and avoidance measures for leakage caused by the failure of sealing gaskets: If we know the cause of the leakage, we need to start from two aspects to cure this problem: first, how to reduce the leakage cross-sectional area, and second, reduce the power of the leakage. Overall increase in flow resistance.

The best way here is to use a sealing gasket, because after applying sufficient pre tension to the sealing surface, the sealing gasket can undergo plastic deformation. When the stress increases enough to cause significant plastic deformation on the surface, it can fill the gap on the sealing surface and block the leakage channel.

The purpose of using gaskets is to utilize the characteristic of gasket materials that are prone to plastic deformation under compressive loads, so as to fill in the small unevenness of the flange sealing surface and achieve sealing.