A mechanical seal is a set consisting of two sub-assemblies that provides sealing efficiency between the rotary part and the stationary part and is generally used to seal shafts in pumps, agitators, etc.

The basic principle is common to all mechanical seals: provide sealing efficiency between two moving faces, lubricated by a liquid film, the so-called primary sealing.

• The film maintained by the rotation comes from the medium conveyed by the machine or is an auxiliary fluid.
• An insignificant part of the film may flow out of the friction faces: this flow is called the consumption of the seal.
• The friction, at the level of the film, produces calories that heat the friction faces, the film itself and the surrounding fluid.
• To ensure optimum seal face service life, the film must be stable and liquid.
• To prevent it from vaporising, the fluid to be sealed should have a sufficient pressure at the level of the seal faces.

Depending on the service conditions, the nature of the fluid and the industrial applications, there are three types of seals (two-component or cartridge seals in single or dual configuration).  Depending on the applications, unbalanced (U) or balanced (B) may be used.

Secondary sealing is ensured by O-rings, elastomer bellows, welded or hydroformed metal bellows that provide leakproof connection between the friction faces and holders.

Depending on the design, other adaptation elements may be associated to the sub-assemblies (sleeves, flange, cover, drive ring, etc.)