Analysis of Sealing Principle and Failure Types of O-Ring Mechanical Seal

Mechanical seal is a mechanical device that prevents leakage by relative sliding of end faces perpendicular to the axis and sealing with auxiliary seals based on the magnetic (or elastic) force of the compensation mechanism and the fluid pressure. It is also called a end face seal or an axial end face seal. This article analyzes the principle of mechanical seal and provides the basic theory of O-ring seal, focusing on the compression ratio of O-ring and the failure type analysis of O-ring mechanical seal.

Principle and failure types of mechanical seal

Because mechanical seals usually work in harsh environments and encounter various problems, some factors may be overlooked in simulation analysis. Therefore, some assumptions can be made:

• The sealing pair structure is axially symmetric, and the load also has this characteristic;

• When the sealing pair works normally, the friction coefficient is a fixed value, and the material wear can be ignored;
  

• The physical properties of the sealing pair material have little to do with temperature and force;
  

• Heat conduction between materials can be ignored;
  

• It is assumed that heat transfer is generated by friction between sealing surfaces, and the distribution of heat flux density on the sealing end faces is balanced.
  

Failure types of O-ring mechanical seal

Permanent deformation

Because the material usually used for O-ring mechanical seal has viscoelasticity, its rebound blocking ability and the initial value used for a long time cause permanent deformation, which gradually disappears and eventually causes leakage.

Clearance bite

Under high pressure conditions, the structure being sealed will have problems such as large inner diameter expansion, low geometric accuracy, and different axes of components, and all of these will cause the sealing ring to be squeezed out and lead to increasing distance of sealing clearance. The hardness value of the O-ring mechanical seal ring also affects the extrusion situation of the clearance. The hardness value of the material is inversely proportional to the pressure of the medium, and directly proportional to the extrusion phenomenon of the clearance.

Distortion

Distortion caused by twisting of O-ring mechanical seal occurs more often in dynamic sealing situations.

Accurate analysis of mechanical seal presents many difficulties and challenges. The computational analysis of previous sealing characteristics is usually obtained by repeated experiments. Therefore, this kind of evaluation cannot evaluate the sealing characteristics deeply, because this evaluation mainly relies on the experience accumulated by researchers for many years, which not only hinders the technical improvement but also cannot meet the engineering requirements.