According to different working conditions and medium properties, mechanical seals include high temperature and low temperature resistant mechanical seals, high pressure resistant and corrosion resistant mechanical seals, particle resistant mechanical seals and mechanical seals suitable for light hydrocarbon media that are easy to vaporize. Choose mechanical seals of different structural types and materials for different purposes. According to the pressure of the sealed cavity, determine the seal structure to adopt balanced or unbalanced, single-end or double-end, etc.; according to the working speed, determine the use of rotating or static, fluid Dynamic pressure or non-contact type; according to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal circulation protection system such as lubrication, flushing, heat preservation, cooling, etc.; determine the use of more Spring or single spring or wave spring, internal or external.