Optimally designing mechanical seals

Several factors play a role in the selection of a mechanical seal, the mechanical seal type, the materials used, and the manner in which a mechanical seal will be operated: process conditions, sealing point where the mechanical seal will be used, operating conditions, and the medium to be sealed. Every system will only work as well as its individual components. If one mechanical seal functions smoothly, then it will lead a largely uneventful life. But as soon as the leakage rate rises or if the mechanical seal even fails, its importance quickly becomes self-evident. Mechanical seals are therefore very important in terms of process stability, plant safety, and economic viability.

IMPORTANT FACTORS AND COMPETENCIES FOR THE SELECTION OF MECHANICAL SEALS

 

Elements of a mechanical seal

The me­chan­i­cal seal es­sen­tially consists of two flat, annular sliding surfaces that are pressed together. One sliding surface is fixed to the sta­tion­ary machine casing, while the other sliding surface is fixed to the rotating shaft. The medium to be sealed, which is gen­er­ally in contact with the outer edge of the sliding surfaces, pen­e­trates the gap between the sliding surfaces, forming a lu­bri­cat­ing film, and emerges at the inner edge as leakage. The pressure dif­fer­en­tial to be sealed is es­tab­lished in the radial di­rec­tion. In its simplest form, a me­chan­i­cal seal can be imagined as a collar that is arranged on, and rotates with, the shaft.

Definition of mechanical seal (abbreviated GLRD)

A me­chan­i­cal seal is a machine element made to seal the passage point of a rotating part (usually a shaft) through a wall (usually the machine casing). Features of the me­chan­i­cal seal are two surfaces sliding on each other – usually arranged at right angles to the ro­ta­tional axle – which are pressed together by axial forces. Between the sliding surfaces is a liquid or gaseous lu­bri­cat­ing film.

Every me­chan­i­cal seal pos­sesses five basic elements:

1. One ring (usually the seal face) circulating synchronously with the rotating part (shaft)
2. Secondary seal (usually O-ring) between shaft and ring
3. A stationary ring (usually the stationary seat) arranged in the stationary part (casing)
4. Secondary seal (usually O-ring) between these parts
5. Spring for the seal face