(1) The sealing surface is opened
In repairing mechanical seals, 85% of seal failures are not caused by wear but by leakage prior to wear.
When the sealing surface is opened, 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 damages the surface of the hard ring.
Because the moving ring or rubber ring is fastened to the shaft (axle sleeve), when the shaft series moves, the moving ring can not be timely attached, so that the sealing surface is opened, and the lag closure of the sealing surface, so that solid particles enter the sealing surface.
At the same time, there are solid particles between the shaft (shaft sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (relative dynamic sealing point, common fault). In addition, the medium will also produce crystals in the friction between the rubber ring and the shaft (shaft sleeve), and there will be solid substances in the spring, which will make the sealing surface open. Mechanical seal
(2) Overheating
Because the sealing surface will generate heat, so the rubber ring temperature should be lower than the design specification. The use temperature of fluorine rubber and ptfe is 216℃, the use temperature of butadiene rubber is 162℃, although they can withstand higher temperature, but because of the heat generated by the sealing surface is higher, so the rubber ring has the risk of vulcanization, and eventually lose elasticity and leakage. (Consider cold brittleness in cold area)
Between the sealing surface will also cause the crystallization of the medium due to heat, such as carbon, resulting in the sliding parts are stuck and the sealing surface is condensed. And some polymers because of overheating and coking, some fluids because of overheating and lose lubrication and even flash fire.
Overheating not only changes the condition of the medium, but also increases its corrosion rate. Cause the deformation of metal parts, alloy surface cracking, and some coating cracks, the design should choose balanced mechanical seal, in order to reduce the specific pressure to prevent overheating.
(3) Out of tolerance
Correct assembly tolerances are necessary for the installation of mechanical seals, and the shaft (bushing) must have the right surface roughness and correct dimensions, but manufacturers rarely provide tolerance data, which are critical for installation. (Rely on experience and common sense)
The dimensional accuracy and shape and position tolerance of mechanical seals must meet the requirements of the drawings, out-of-tolerance will lead to premature seal failure.