(1) the sealing surface is opened
In the repair of mechanical seals, 85% of the sealing failure is not caused by wear and tear, but before wear, it has leaked.
When the sealing cover is opened, the solid particles in the medium under the action of liquid pressure into the sealing surface, the sealing surface is closed, the solid particles embedded soft ring (usually the right ink ring) on the surface of it into a "wheel" will damage the hard surface.
Because the ring or rubber ring fastening on the shaft (sleeve), when moving, moving ring can not be fit, and the sealing surface and sealing surface of the open, closed backward into the sealing surface, made of solid particles in.
At the same time, there are solid particles between the shaft (shaft sleeve) and the sliding parts, which affect the sliding of rubber ring or moving ring (relative dynamic sealing point, common faults). In addition, the medium will also produce a crystal in the rubber ring and the shaft (shaft sleeve), and there will be solid substances at the spring, which will make the sealing cover open.
Because of the heat on the sealing surface, the temperature of the rubber ring should be lower than the design specification. The use of fluorine rubber and PTFE temperature is 216 DEG C, the use of NBR temperature is 162 DEG C, although they are able to withstand the high temperature, high heat but because the sealing surface is generated, so the rubber ring is dangerous to sulfide, eventually lose their elasticity and leakage. (cold zone is cold and crisp)
The sealing surface will also cause crystallization of the medium due to heat, such as carbon deposition, which causes the sliding parts to be stuck and the sealing surface to be condensed. In addition, some polymers are coking because of overheating, and some fluids lose lubrication and even flame when overheated.
Overheating can increase the corrosion rate as well as change the condition of the medium. The deformation of the metal parts, the cracking of the alloy surface and the cracks in some of the coatings, the design of balanced mechanical seals should be adopted to reduce the specific pressure and prevent overheating.
(3) over tolerance
Tolerance is correct, it is necessary for the installation of mechanical seal, shaft (sleeve) must have the appropriate surface roughness and the correct size, but the manufacturer provides little tolerance data, these data is key to the installer. (relying on experience and common sense)The dimension accuracy and form tolerance of the mechanical seal must comply with the requirements of the drawing, and the over tolerance will lead to premature sealing failure.