Sealing systems are supposed to seal off the rotating shaft against the surrounding environment. When selecting a suitable seal for pump shafts between the atmosphere and the working fluids, it is important to consider the hazard potential. TA Luft (German clean air regulations), the maximum workplace concentration or Atex guidelines, for instance, describe the requirements for shaft seals and specify their technical data. Sealing systems for innocuous media represent the biggest group. A stuffing box (possibly in combination with a hydrodynamic seal), magnetic coupling, canned motor or mechanical seal may be used for this purpose. Labyrinth seals which are open to the outside environment with pumping and locking devices, stuffing box packings made from different materials and lubricated with water, grease or graphite and shaft seal rings are three popular choices. Three approved systems remain for fluids with medium to high hazard potential, namely double mechanical seals, magnetic couplings and canned motors. Double mechanical seals are generally liquid-lubricated. Their disadvantage is that they require a sealing system. This is a complex task and the maintenance costs are high. Magnetically coupled pumps can often be a good alternative.
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