One of the mysteries associated with Mechanical Seal Repair is "When is my mechanical seal suitable for repair?" Often times the seal looks good to the naked eye, but when it gets to a repair center the comment comes back "This seal is non-repairable." Metal bellows seals need to be pressure tested before repairability can be determined. Mechanical seals all have the same single issue regardless of brand or design. They all have one primary wear point, the seal faces. Like tires treads, seal faces wear from rotational contact. And like tire treads seal faces wear down and eventually fail. Carbon is the most common sacraficial seal face and is used due to it's low frictional characteristics. Less friction means less energy consumed by the pump. If you remove your seals due to leakage after a short life span, it's likely time to look at other seal face materials such as Silicon Carbide, Tungsten Carbide.
Obvious catastrophic damage to the seal such as a broken sleeve or an extremely eroded gland would indicate that you may have significant problems that would prevent a repair. If you have more pieces of the seal come out of the pump than went in would indicate a non-repairable situation. The best thing to do is have a trained mechanical seal specialist evaluate the seal. Even a seal that looks hopeless externally can sometimes be brought back to new condition for relatively little money.
All mechanical seals function basically the same way. Two mating faces contact each other forming a seal at the mating surface. Usually one surface is made of a soft material such as carbon and the other surface is made from a hard material such as silicon carbide. A series of O-rings or other sealing materials form seals on the shaft and gland area. Everything is held in the stuffing box by a gland of some sort. Depending on the design of the mechanical seal, everything may be mounted on a sleeve and cartridge mounted to incorporate the gland into the seal itself.
The most important thing to do first is choose a company that has a good reputation for quality repairs and ethical business practices. There are many companies today that claim to bring seals "up to the original equipment manufacturer's standards," but they use inferior materials that result in shorter product life and in some cases, cause serious damage to the pumping equipment. Research carefully the facility doing the repairs to ensure that it has the latest manufacturing and testing equipment. On-site engineering capabilities and tools, such as finite element analysis, lead to better overall repair companies. If the company you choose is sending the seal components to outside sources to be refurbished, audit the sources to ensure you are getting a quality repair.
Often, the best source for repairs is a company that does everything in-house including manufacturing, assembly, and testing. This ensure that you have product integrity throughout the process.
The first step in repairing any mechanical seal is documenting the seal properly--where it came from, the service it is in, and any other comments that may have come from the user company. The next step is to disassemble and clean the seal completely for inspection. After the seal has been inspected a list of components necessary for a mechanical seal rebuild can be created.Reprint from May 1997 Plant services
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