Mechanical Seal Systems How to Select the Right Seal for Mixing Applications

Author / Editor: Bernd Reichert / Dr. Jörg Kempf

The basic sealing task in mixing applications is to seal the rotating shaft as it passes through the vessel wall. Depending on the operating conditions — pressure, temperature, agitator speed, etc. — different types of seals are used. As this article shows, mechanical seals offer many advantages over other types of seals. Particularly if hazardous or explosive substances are being mixed, a mechanical seal is mandatory.

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Mechanical seal system
Mechanical seal system
(Picture: Ekato)

Mechanical seals are generally regarded as mechanical engineering components, and are used e.g. in pumps as a sealing component. The situation is somewhat different in processes and applications of mixing technology. In these cases, the mechanical seal is generally implemented as a unit that can be exchanged. These are referred to as “cartridges”. Whereas single-acting mechanical seals still have a component character, double- and triple-acting mechanical seals are regarded as mechanical seal systems owing to their complexity.

A mechanical seal system consists of the mechanical seal cartridge, the hydraulic components (e.g. pressure compensator) and the “installation”, which comprises the piping, instrumentation and mountings. In some cases, this also includes a seal liquid refilling system, as shown in Fig. 2 (see picture gallery).

Gallery with 11 images

As a consequence, in most mixing systems, only the complete mechanical sealing system can provide reliable sealing of the vessel. The sealing function of the vessel can be guaranteed and maintained if the mechanical sealing system has been correctly selected.

Supply Systems — What are the Tasks?

Supply systems ensure safe and reliable operation of the mechanical seal. A seal is regarded as being technically sealed when the pressure in the seal liquid chamber is always higher than the vessel pressure. The supply of seal liquid is thus of primary importance to safety.

Supply systems must be able to fulfill the following tasks in order to guarantee a reliable mechanical seal operation: See next page ...