How are made mechanical seals, and how do they work in pumps? When I first started working as a technician, I was wondering how it was possible for a mechanical seal to avoid leakages of fluids on a rotating shaft. This is in fact the purpose of a mechanical seal, to avoid the leakage of liquids on a rotating part, functioning as a seal where there is a rotor that gets water under pressure.
And so, how is made a mechanical seal? A mechanical seal is basically made by two parts, one fixed and one rotating. The fixed part is mounted on the main body pump, it achieves sealing through an O-ring and has a grinded and very smoothed surface that gets in direct contact with the mobile part.
The rotating mobile part is mounted on the shaft, and so this is integral with it. Also in this case, sealing is achieved with an O-ring, so a classical seal, on the shaft side. The seal between the two parts is ensured by the contact between the surfaces that are so very much smooth that avoid any fluid’s leakage, being it both water or oil.
Mechanical seals can be made in different materials, depending on the kind of fluid to be pumped and also on the temperature levels involved. Based on the type of fluid treated, and with increasing temperatures for example with oil and aggressive fluids, the constructive materials of the seal must ensure the proper resistance.
The materials undergo a very high friction: in fact, a two pole pump works at 2.900-3.000 rpm, generating a very high rubbing between the two parts. That’s why mechanical seals are usually cooled by the fluid itself or, in more extreme applications, by fluxing systems aimed to maintain temperatures at affordable levels.
The fluxing of the seals is not only necessary to maintain temperatures at acceptable levels, but also to create a lubrication layer, let’s call it like this, between the two surfaces. With the rotating speeds involved, and being the surfaces so much smooth, without a proper lubrication the two surfaces could seize up indeed, and therefore get ruined and causing a leakage in the seal.
Finally, during the substitution of a mechanical seal, always remember to change also the seal on the main body of the pump.
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