Basic structure of mechanical seals, their functions, and requirements

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Mechanical seals are mainly composed of a rotating ring, a stationary ring, a cooling device, compression springs, sealing rings, fasteners, and other components. 　　1. Face seal pair of mechanical seals (static ring, dynamic ring) – The face seal pair ensures that the sealing surfaces are in close contact, thereby preventing leakage of the medium. It requires that both the stationary ring and the rotating ring have good wear resistance. The rotating ring can move axially with flexibility, automatically compensating for wear on the sealing surface so as to ensure a good fit with the stationary ring; the stationary ring has a floating property that serves as a buffer. To this end, the sealing surface requires high-quality machining to ensure good fit between the sealing components. 　　2. Elastic elements of mechanical seals (springs, bellows, diaphragms) The elastic elements serve primarily to provide pre-tension, compensation, and cushioning. They must maintain sufficient elasticity to overcome the friction caused by the auxiliary seals and driving components, as well as the inertia of the moving ring, thereby ensuring good contact between the face seals and enabling the moving ring to move smoothly. The materials used must be resistant to corrosion and fatigue. 　　3. Auxiliary seals for mechanical seals (O-rings, V-rings, U-rings, wedge rings, and custom-shaped rings). The auxiliary seals serve primarily to seal the stationary ring and the rotating ring; they also provide floating and cushioning functions. The sealing elements of the stationary ring are required to ensure sealing between the stationary ring and the gland, as well as to allow a certain degree of movement for the stationary ring. The sealing elements of the rotating ring are meant to ensure sealing between the rotating ring and the shaft or shaft sleeve, while also permitting some movement for the rotating ring. The materials are required to be heat-resistant, cold-resistant, and compatible with the medium. 　　4. Transmission components of mechanical seals (transmission pins, transmission rings, transmission seats, transmission keys, transmission lugs, or spline couplings). These transmission components are used to transfer the torque from the shaft to the moving ring. The materials are required to be wear-resistant and corrosion-resistant. 　　5. Fasteners of mechanical seals (set screws, spring seats, gland plates, assembly sleeves, shaft sleeves) – These fasteners are used to position and secure the stationary and rotating rings. It is required that the axial alignment be correct, so as to ensure a certain degree of spring compression; this allows the sealing surfaces of the sealing pair to be in the proper position and maintain good contact. It is also required to be easy to assemble and disassemble, to fit in easily, and to be reusable. At the interface with the auxiliary seal, the sealing ring installed there should have guiding chamfers and a certain degree of compressibility. Special attention must be paid to the requirement that the auxiliary seal component on the moving ring and the shaft sleeve must be wear-resistant and corrosion-resistant; where necessary, a hard-coated layer can be used at the interface with the shaft sleeve. 　　6. Anti-rotation element (anti-rotation pin) of mechanical seals – The anti-rotation element is used to prevent the stationary ring from rotating or coming loose. It is required to have sufficient length to prevent the static ring from coming loose under negative pressure, and it must be properly positioned to prevent the static ring from rotating along with the moving ring. The material is required to be corrosion-resistant; if necessary, a tetrafluoroethylene sleeve can be added in between to prevent damage to the carbon-graphite static ring.