Mechanical seals

A mechanical seal is an assembly composed of two sub-assemblies ensuring sealing between a rotating part and a stationary part. It is primarily used to seal shafts of pumps, agitators, mixers, and many other industrial equipment.

The operating principle is identical for all mechanical seals: to ensure sealing between two moving faces thanks to an extremely thin liquid film called primary sealing.

This film, maintained by the rotation of the equipment, comes either from the fluid conveyed by the machine or from an auxiliary fluid. A very small quantity of this film may escape outside the friction faces: this controlled leakage corresponds to the normal consumption of the mechanical seal.

The friction generated at this film produces heat, which is dissipated by the surrounding fluid. To ensure optimal service life of the friction faces, this film must remain stable and in a liquid state. To prevent vaporization, the fluid pressure at the faces must be sufficient.

Depending on the operating conditions and the nature of the fluid to be sealed, several technologies can be used:

• Liquid-lubricated mechanical seals: The friction faces are lubricated directly by the process fluid or by an auxiliary fluid to ensure cooling and lubrication.
• Dry mechanical seals: Also known as unlubricated or contacting mechanical seals, they are used in certain specific applications where liquid supply is not possible.
• Gas mechanical seals: These seals operate without contact between the faces thanks to a gas film, limiting friction and wear.

Depending on requirements, seals can be offered as bi-component or cartridge types. They can also be balanced (B) or unbalanced (U) depending on the pressure levels encountered.

Secondary sealing is provided by O-rings, elastomeric bellows, or welded or hydroformed metal bellows. Depending on the design, various complementary elements can be associated with the seal: sleeves, flanges, covers, drive rings, or specific adaptation parts.

The selection of a mechanical seal is based on several operating parameters that must be analyzed jointly.

• The fluid to be sealed: The nature of the fluid is an essential criterion. It is particularly important to consider: its abrasiveness, corrosivity, viscosity, volatility, toxicity, pH, concentration, the possible presence of crystals or suspended solids, and pressure.
• Operating pressure helps determine the type of seal to use: Unbalanced seal (U) for pressures generally below 10 bar, balanced seal (B) for pressures above 10 bar.
• Rotational speed: A mechanical seal must remain stable at the machine’s operating speed. Geometric defects in the equipment can significantly influence the behavior of the film between the friction faces. For high speeds, generally above 20 m/s, stationary seals are often preferred because they are less sensitive to centrifugal effects.
• Temperature: All components of the mechanical seal must retain their properties across the entire operating temperature range. The choice of materials for the friction faces, secondary seals, and metallic components directly depends on this parameter.

The materials constituting the friction faces are selected based on their mechanical, thermal, and chemical characteristics, as well as their ability to function together under optimal lubrication conditions. Depending on the applications, mechanical seals can be equipped with faces made of Silicon carbide, tungsten carbide, graphite, or carbon to achieve the expected Performance in terms of service life and reliability.

LATTYseal B 24610 U6 U6 V4 = mechanical seal type 24610 balanced (B) with friction face in pure Silicon carbide (U6) / pure Silicon carbide (U6) and FPM FDA seal (V4)