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Gasket To Maintain A Good Seal
Jun 19, 2017

Sealing gasket is to prevent leakage, specifically to prevent the liquid or gas through the gasket seal connection leakage, for the pump gasket seal, the main seal of the medium is generally liquid, gas or dust. Then affect the gasket seal leakage mainly in the following two cases: First, there is a gap on the sealing surface. Second, there is pressure on both sides of the sealing site. The gasket seal needs to be addressed by eliminating or reducing the gap between the sealing surfaces. This gap includes the gap between the sealing surfaces and the gap inside the seal. The reasons for the leakage of the gasket are mainly due to the following.

1, the impact of the compression stress on the gasket

In order to achieve the sealing effect, it is necessary to apply a sufficient pressure to the sealing gasket so that it can be elastically or plastically deformed to fill the uneven surface of the sealing surface. But when the assembly is not achieved due to the required clamping force of the gasket, or long-term operation of the mechanical vibration of the compression bolts loose, in addition to the aging of the gasket material and the loss of the original elasticity will make the gasket failure Produce a leak. If the gusset's compression stress is too large, it is particularly easy to crush the gasket, thus losing the resilience, can not compensate for the temperature, pressure caused by the flange surface separation, resulting in a sharp increase in leakage rate. So to maintain a good seal, the pad must be to maintain the stress in a certain range of stress.

2, gasket material within the organization or uneven thickness

The cardboard with cracks or wrinkles causes the gasket itself to form a gap, and leakage is unavoidable when the force acting on the gasket causes the elastic deformation caused by the gasket to be insufficient to completely fill the gaps.

3, gasket sealing the working conditions

Different pressure, temperature, the leakage rate of different sizes. The pressure difference on both sides of the sealing surface is the main driving force of the leakage, the greater the pressure difference, the easier the media to overcome the leakage channel resistance, the easier the leak. The temperature has a significant effect on the sealing performance of the connecting structure. The results show that the elastic deformation of the gasket increases with the increase of the temperature, while the rebound performance decreases with the increase of the temperature, and the creep increases with the temperature increasing. And with the temperature rise, the gasket aging, weight loss, creep, relaxation will become more and more serious. In addition, the temperature of the medium viscosity also has a great impact, with the temperature rise, the viscosity of the liquid decreased, while the viscosity of the gas increased. The higher the temperature, the more prone to leakage.

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

Due to the diversity of the chemical properties of the chemical products delivered by the pump, and the addition of some minor additives to the fuel in order to increase the combustion value of the fuel or to change its post-combustion product, the properties of the fuel change, It is not easy to select the gasket material that is compatible with the media, and it is often the case that the gasket is eroded due to incompatibility.

5, the impact of gasket material size

A, the impact of the thickness of the gasket: the same compression load, the same medium pressure, the leakage rate with the pad thickness increases. This is due to the fact that under the same axial load, the thick washer has a large amount of compressive rebound, and in the case where the initial sealing condition has been reached, the thicker gasket with greater elasticity is more compensated by the thin pad The relative separation of the sealing surfaces caused by the medium pressure and the retention of the residual compressive stress on the surface of the gasket, thereby reducing the leakage rate. The thickness of the gasket is different and the initial sealing condition is different. Due to the influence of the friction on the end face, the surface of the gasket is in a three-way stress state, and the deformation resistance of the material is large. Smaller, the deformation resistance is also smaller. In the same preload, the middle of the gasket is more prone to plastic deformation than the surface of the gasket. At this time, it is 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 pad, the greater the area of osmotic leakage, the greater the leakage rate.

B, the impact of the width of the gasket: in a certain range, with the gasket width increases, the leakage rate was linear decline. This is because the medium leakage resistance in the effective width of the gasket is proportional to the length of the leak channel (proportional to the width of the gasket). But can not say that the wider the better the gasket, because the wider the gasket, the greater the surface area of the gasket, so the same pad to produce the same stress, wide gasket bolts will be narrow Much more.

Leakage is essentially a movement of space in space, that is, from a limited space to an infinite space, or from an internal flow to the outside, and vice versa. The reason why the medium flows between the two is to leak the power source of the province. Leakage usually occurs at both ends of the interface, and there are two conditions: First, the cross-sectional area at which the leak is available at the junction, There is a certain pressure difference or poor concentration at both ends.

First of all, any equipment or mechanical processing will exist more or less the accuracy of the problem, the sealing surface will inevitably appear gap, it is difficult to achieve a complete fit, especially when the contact surface hardness is high, there is no plastic deformation Time, such as the connection of flange joints, and media, especially gas, liquid superiority all-pervasive. So the leak will inevitably occur.

Sealing gasket failure to produce the reasons for the leak and to avoid the initiative: to know the reasons for its leakage then cure this problem will start from two aspects, one is how to reduce the leakage cross-sectional area, and second, to reduce the leakage of power. The overall increase in resistance to flow.

The best way here is to use a gasket because the gasket can undergo plastic deformation after applying sufficient preload to the sealing surface. When the stress increases enough to cause the surface to produce significant plastic deformation, you can fill the gap of the sealing surface, plug the leakage channel.

The purpose of the use of gasket is the use of gasket material under the action of the compression load is more likely to produce plastic deformation characteristics, so that the flange sealing surface of the small bumps, in order to achieve sealing.

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