mechanical sealings & other sealings

What are mechanical seals used for?

Mechanical seals are dynamic seals, so they seal a rotating shaft against a wall, e.g. B. a machine housing. The main components are two components sliding on each other, the spring-loaded slide ring (position a in the upper picture) and a counter ring (position d in the upper picture). One of the two rings sits rigidly in the stationary housing (stator), the other is attached to the rotating shaft by means of anti-rotation pins (rotor). The areas between these two parts are - depending on the type of mechanical seal - mostly flat and usually consist of carbon-graphite materials, metal, ceramic, plastic or resin-bonded carbon.

Advantages of mechanical seals over stuffing box housings?

Mechanical seals are more costly to procure, but they bring many mechanical advantages over the classic stuffing box packing. First, there is no need for a shaft protection sleeve to protect the shaft from overheating, since the seal does not go directly over the shaft. Sealing water is rarely used for mechanical seals. Despite the perfectly adjusted stuffing box, the sealing water can dilute the medium. At the same time, emerging sealing water can enter the bearing and thus greatly reduce the life of the bearing. This is not the case with a mechanical seal. Packing cords also get hot and can burn out if the packing glasses are tightened too much. Especially when it comes to pumps that do not run 24 hours a day. Here it can happen that the seal dries out and no longer seals properly. The result is severe pollution of the environment, possible early damage to the bearing due to contamination of the lubricant by water, and calcification or corrosion of the housing and a subsequent failure of the machine.
The mechanical seal is preloaded with a spring and the sealing surfaces always sit on one another with the right pressure. No leakage, no contamination of the lubricant in the bearing, no damage to the bearing too early, fewer machine failures and this results in economical operation even if the initial costs are higher at first glance.