It is known that a mechanical seal is a complex device in its design, assembly and functioning. Nevertheless, its efficacy does not often depend on any of the aforementioned points but on another one, which is not always considered: the state of the installation of mechanical seals for pumps.
The state of the installation and the shaft where the seal must be assembled is determining for the mechanical seal’s proper functioning. It is common for these components of the pumps to suffer from wear and damage at the time of the repair.
The first element that must be revised to ensure the proper functioning of the mechanical seal is the shaft. The shaft must have the correct tolerance, no scratches or any small orifices produced by wear. It is common for the seal’s O-ring supposed to be replaced to leave a mark, or in very extreme cases, a groove, in the area where it has been working. This is especially the case when dealing with dynamic O-rings such as the one found in ‘pusher’-type seals, like the LWS10.
This type of damage is less common if a cartridge or a LMB85 seal have been used.
The next component of the system that we must revise is the installation of the seat part. It is not uncommon to find corrosion, embedded residues and erosion produced by the work of the joint. The installation must have the proper dimensional tolerance and roughness and be free of residues.
If a cartridge seal is being assembled, it is vital that the surface where the flat joint of the seal is supposed to work is in prime condition, without any sign of corrosion and completely smooth.
Finally, the most important factor to ensure the proper functioning of a seal is the alignment of the shaft. This must be completely centred and turn without eccentricities or axial shifts. The incorrect alignment of the shaft is one of the most common causes of failure in mechanical seals and cartridges, with the aggravating circumstance that the work on said machines usually damages the seal irreparably.
Consequently, it is important to revise the state of the bearings and, if necessary, to replace them before changing the mechanical seal. This principle is also applicable to other sealing systems, such as retaining elements or packing.
