There are three main reasons for the failure of sealing function of mechanical seals

(1) Secret cover open

When repairing mechanical seals, 85% of the seal failure is caused not by wear, but by leakage before wear.

When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of liquid pressure, and when 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 hard ring surface.

Because the dynamic ring or rubber ring is fastened to the shaft (bushing), when the shaft is strung, the moving ring can not be fitted in time, and the dense cover is opened, and the hysteresis of the sealing surface closes, so that the solid particles into the sealing surface. At the same time, there are solid particles between the shaft (bushing) and sliding parts, which affect the sliding of rubber rings or moving rings (relative dynamic sealing points, common faults). In addition, the medium will also be in the rubber ring and shaft (bushing) friction area to produce crystallization, in the spring will also have solid substances, will make the dense cover open.

Mechanical Seals

(2) Overheating Because heat will be generated on the sealing surface, the use temperature of the rubber ring should be lower than the design specification. Fluorine rubber and PTFE use temperature of 216 ℃, butyl rubber use temperature of 162 ℃, although they can withstand higher temperatures, but because the sealing surface produces higher heat, so the rubber ring has the risk of continued vulcanization, and eventually loss of elasticity and leakage.(Cold zone considering cold and brittle) The crystallization of the medium is also caused by heat in the sealing surface, such as carbon, causing the sliding parts to be glued and the sealing surface to be condensed.

And some polymers are coking due to overheating, some of which lose lubrication and even flash fire due to overheating. Overheating, in addition to changing the condition of the medium, can also exacerbate its corrosion rate.

caused by the deformation of metal parts, the cracking of alloy surface, as well as some coating cracks, the design should choose a balanced mechanical seal, in order to reduce the specific pressure to prevent overheating.

(3) Extremely poor Correct assembly tolerances are necessary for the installation of mechanical seals, the shaft (bushing) must have the right surface roughness and the correct size, but the manufacturer rarely provides tolerance data, which is critical for installation.

(relying on experience and common sense) The dimensional accuracy and shape tolerance of mechanical seals must conform to the drawing requirements, and the variance will lead to the early failure of the seal.