Secondary Seals in the Dynamic Characteristics of Non-Contact Mechanical Seals

The dynamicproperty of mechanical seals is the key to keep end faces non-contact, which have a considerable impact on the safety and effectiveness of the system. The secondary seals, which are usually made of flexible elements, mainly synthetic rubber O-rings, have a variety of nonlinear characteristics and take important roles in the dynamic property of mechanical seals. Due to the lack of attention to the secondary seals, there are still many leakage problems caused by the poor following abilities of them. Sorting and compiling the history of secondary seals will help to improve the dynamic performance of the sealing system. This paper provided a summary of the main kinetic models of mechanical seals to introduce the major variables influencing the dynamic features. The friction, stiffness and damping were the main parameters. Contact, which was the basis of friction, was usually studied by semi-empirical models and numerical simulation models. The combination of them was expected to obtain accurate contact pressure distributions. The friction of secondary seals was influenced by the environment, materials, surface properties and so on. Because of the viscoelasticity of rubber materials, the friction of the secondary seal had hysteresis nonlinearity, which was one of the key causes of instability in the sealing system. In order to improve the following performance of the primary seal, the key and recent subjects in the research on secondary seals in terms of dynamic characteristics were also compiled and summarized. Experimental methods were the primary way for measuring stiffness and damping of secondary seals, including the base excitation resonant mass (BERM) test method and the relaxation test method. The stiffness and damping of the secondary seal were related to parameters such as sealing pressure and speed. However, they were expressed as constant values in the kinetic model, ignoring the influence of the change of working conditions, which was not consistent with the actual working condition. In addition, the effects of rubber aging problems were not considered. It was not conducive to study the following performance of the compensation ring. The main purpose of the optimization of the secondary seals was to reduce the friction damping and improve the dynamic performance of the seal system, which was mainly carried out in terms of the secondary seal structures, the mounting grooves, and the parameters of the tribological characteristics. Small compression ratio, good lubrication, and the right materials could reduce friction damping. In summary, the researches on each part of the secondary seals were relatively independent, and the nonlinear characteristics of material, friction and stiffness and damping were not sufficiently considered in the studies of the dynamic characteristics of the seal systems. In the future, the researches on secondary seals could focus on the ontological relationships and the nonlinearities of the friction, stiffness and damping.