Mechanical seals are used mainly in pumping applications (although the principles are the same for mixers, blowers and compressors). In essence, the pump has two main elements; the first being a rotating shaft and the second being the pump casing. Without a seal, the pumped medium (water, waste, oil, etc) would leak and the pump would be ineffective. The mechanical pump therefore creates the seal between the moving part (dynamic) and the stationary part (static). Because of this Mechanical seals are often called many things including shaft seals, pump seals, rotary shaft seals, water pump seal and combinations of these. Whatever you call it, the product is essentially the same.
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Mechanical seals or more technically “end face mechanical seals” were designed in the early s but really came to prominence during the post-war boom (late s) in both industrial and domestic equipment sales.
The elements of a mechanical seal are what make it unique. They are:
The seal between the stationary component and the rotating component is called the ‘Primary Seal’ and is the most important. However there is a ‘Secondary Seal’, which is typically an O Ring and sits between the rotating component sealing member and the shaft of the pump.
The spring is used to create just the right pressure in the primary seal between the stationary and rotating surfaces.
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The primary seal surface in various mechanical seal types come in a vast array of materials, such as Carbon-graphite, Silicon carbide, Tungsten carbide and Alumina ceramic. The choice of material is dependent on the medium (the liquid to be sealed), the pressures the seal must withstand and the temperatures of the medium. Speak with your mechanical seals supplier to determine the best materials for your application.
Before the invention of mechanical seals, mechanical packings or gland packings were used. These worked well in principle, but had a higher leakage rate (not ideal for some applications) and can handle higher temperatures and pressures (thanks to the sprint component).
Additionally, the use of packing in earlier designs caused shaft and sleeve wear that reduced the life of the pump and increased costs. Mechanical seals therefore improve equipment lifespan.
The other benefit is that they are self-lubricating in that their design specifically allows a very small amount of leakage onto the sealing surface, which lubricates and keeps the primary seal from eroding. Finally, mechanical seals require virtually zero maintenance as they do not require periodic tightening as Gland packing would.
Ultimately therefore, mechanical seals are a simple, elegant and cost effective solution to creating a long-life seal in dynamic applications.
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