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Mechanical Seals

Split Mechanical Seal

Split Mechanical Seal

What can be said in favor of these seal types? They are riddled with potential leak paths. All the components of the seal are supplied either cut, to be joined on site, or in halves. In addition to the normal fitting problems, you have the additional task of ensuring that all the seal elastomers are properly butted and sealed, that the stationary and rotating faces are accurately aligned with the mating half, as well as with each other, and often the recommended application is an emergency situation where no alignments are guaranteed on the pump in any circumstances.

The only time I could recommend such a seal is as an emergency repair for a leaking gland. It is not a suitable seal for permanent use. They can be recommended as a fix for a leaking packing gland. The split seal is mounted on the shaft external to the gland and runs against the stationary which is mounted on the gland driver. The pump should be taken out of service and overhauled at the first opportunity.

Leak paths

A split seal means that all the parts must be capable of being fitted to a shaft without dis-assembly of the shaft assembly itself. The seal pictured here is one of the best on the market.

But look at it carefully, note all the split components, the o-rings, seal seats, body components ... before it can effect a good seal on the pump unit it has to fight its own construction.  To cap it all you have to ensure that all these fiddly bits of seal, all with their own leak path are fitted exactly, exactly mind you, in place. What are your chances?

OK so consider that seal. The seal head comes in two halves, the O-rings are not rings, the metal parts are split. The stationary parts are also split. The stationary rubber boot, ceramic face, the clamping arrangement are all in two halves to facilitate fitting around the shaft.

The design must ensure that the sensitive face components are fitted precisely and the elastomeric components mate together to prevent leakage. The positioning of the seal on the shaft at the correct fitting length has to be accommodated and finally the design has to cope with the results of earlier leakage and any resulting corrosion of the shaft. Given that seals work in a hostile environment of vibration, mis-alignment, shaft deflection, abrasion, the split seal has even more obstacles to overcome to provide successful service.


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