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What Is The Principle Of Mechanical Seals? Under What Conditions?
Apr 23, 2018

What is the principle of mechanical seals? Under what conditions?

The gap between the seal face and the seal face is the main sealing surface. It determines the key to the friction, wear and sealing performance of the mechanical seal, and also determines the service life of the mechanical seal.

The Seal Face is free to move in the spring-loaded axial direction to maintain contact with the Seat. Axial mobility allows for automatic compensation of wear, eccentricity and thermal displacement of the shaft. The O-ring acts as an auxiliary seal, which acts as a radial seal and cushioning, so that the entire seal does not rigidly contact in the radial direction. In the rest condition, the grinding ring of the moving ring and the stationary ring is in mechanical contact, but when the shaft rotates, the complicated frictional action takes place between the end surface and the fluid being sealed.

The main characteristic of mechanical seals is their automatic interface lubrication mechanism that controls the sealing function, friction, wear and life. Everything depends on the liquid passing through the interface and establishing the lubricating film so that the seal operates under conditions that are virtually non-contact (usually mixed friction, lubricating frictional state between dry friction and intact liquid film).

Under the pressure of the cavity, the medium passes through the seal friction secondary surface; surface tension and centrifugal force have little effect at this time. As the fluid flows radially through the end face, the fluid pressure continues to drop until it reaches an external back pressure (typically atmospheric pressure), which acts similar to the load bearing function of a hydrostatic bearing. The bearing capacity of the seal depends on the pressure difference and the shape change of the interfacial gap. Mathematical analysis is more complicated. Refer to books related to mechanical seals, such as Gu Yongquan and Cai Renliang.

As the seal rotates, the shear flow in the end face interacts with changes in the remaining height of the end face to produce a hydrodynamic pressure that has a similar load bearing function for the hydrodynamic bearing and is dependent on changes in media viscosity, rotational speed, and face gap.

Under normal conditions, the hydrodynamic fluid hydrodynamic pressure field and the hydrostatic pressure field constitute the bearing capacity during seal operation, which is part of the opening force and is used to prevent the rigid contact of the seal. When the opening force and the closing force deviate from the balance, the end faces are automatically adapted to each other or a large number of leaks occur!

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