Since 2006, Focus on rubber seals

Why do seals sometimes fail?

by:ORK      2022-10-17
There are three main reasons for seal failure: 1. The sealing surface is opened. When repairing mechanical seals, 85% of the seal failures are not caused by wear, but have leaked before 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”will damage the hard ring surface. Since the moving ring or rubber ring is fastened on the shaft (sleeve), when the shaft moves in series, the moving ring cannot fit in time, and the sealing surface is opened, and the hysteresis of the sealing surface is closed, so that solid particles enter the sealing surface. . At the same time, there are also solid particles between the shaft (sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (relative to the dynamic sealing point, common failure). In addition, the medium will also produce crystals in the friction part between the rubber ring and the shaft (sleeve), and there will also be solid substances in the spring, which will open the sealing surface. 2 Overheating Due to the heat generated on the sealing surface, the operating temperature of the rubber ring should be lower than the design specification. The operating temperature of fluororubber and PTFE is 216 °C, and the operating temperature of NBR is 162 °C. Although they can withstand higher temperatures, the heat generated by the sealing surface of the seal is relatively high, so the rubber ring has Danger of continued vulcanization, eventually losing elasticity and leaking. (Consider cold brittleness in the cold area) The crystallization of the medium between the sealing surfaces due to heat, such as carbonization, will cause the sliding parts to be stuck and the sealing surface to be condensed. And some polymers coke due to overheating, some fluids lose lubrication due to overheating, etc. and even flash fire. In addition to changing the condition of the medium, overheating will also increase its corrosion rate. Deformation of metal parts, cracking of alloy surfaces, and cracks in some coatings should be used in the design of balanced mechanical seals to reduce specific pressure and prevent overheating. 3. The correct assembly tolerance is necessary for the installation of the mechanical seal. The shaft (shaft sleeve) must have the appropriate surface roughness and the correct size, but the manufacturer rarely provides tolerance data, which are all important for installation. is critical. (Rely on experience and common sense) The dimensional accuracy and geometrical tolerance of the mechanical seal must meet the requirements of the drawings, and excessive tolerance will lead to premature failure of the seal. Company website:
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