(1)The sealing surface is opened　　
       In repairing mechanical seals, 85% of seal failures are not caused by wear, but because they leak prior to wear.
　　When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface is closed, these solid particles are embedded on the surface of the soft ring (usually the right ink ring), which actually becomes a "grinding wheel" that will damage the surface of the hard ring.
　　Because the moving ring or rubber ring is fastened to the shaft (shaft sleeve), when the shaft is connected, the moving ring can not be fit in time, and the sealing surface opens, and the sealing surface lag is closed, so that the solid particles into the sealing surface.
　　At the same time, there are also solid particles between the shaft (shaft sleeve) and the sliding parts, which affect the sliding of the rubber ring or moving ring (relative moving sealing point, common faults). In addition, the medium will also produce crystals in the rubber ring and the shaft (shaft sleeve) friction part, and there will also be solid substances in the spring, which will make the sealing surface open.
　　(2)Superheat
　　Due of heat on the sealing surface, the use temperature of rubber ring should be lower than the design specification. The use temperature of fluorine rubber and polytetrafluoroethylene is 216℃, and the use temperature of fine rubber is 162℃. Although they can withstand higher temperature, the higher heat generated by the sealing surface makes the rubber ring have the risk of continuing vulcanization, and eventually lose elasticity and leak.(Cold and brittle conditions are considered for cooling)
　　The sealing surface will also cause the crystallization of the medium due to heat, such as carbon formation, causing the sliding parts to be stuck and the sealing surface to condense. And some polymers because of overheating and coking, some fluids due to overheating and lost lubrication and even flash fire.
Overheating can not only change the condition of the medium, but also aggravate its corrosion rate. Cause the deformation of metal parts, alloy surface cracking, and some coating cracks, the design should choose a balanced mechanical seal, to reduce the specific pressure to prevent overheating.　　
(3) Overproof
　　Correct assembly tolerance is necessary for the installation of mechanical seal. The shaft (shaft sleeve) must have the appropriate surface roughness and correct size, but the manufacturer rarely provides tolerance data, which is critical for the installation.(Relying on experience and common sense)
　　The dimensional accuracy and shape tolerance of mechanical seals must meet the requirements of the drawings, and the deviation will lead to early failure of the seal
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