What are the advantages of bellows mechanical seals?

Advantages of a Bellow Mechanical Seal

A Bellow Mechanical Seal is a seal assembly comprising a radially disposed of bellows unit and a cartridge sleeve that is permanently secured to the bellows unit by a circumferential weld. Prior to being permanently fixed, the bellows assembly and the corresponding cartridge sleeve are lapped and flatness checked so that both components remain perfectly flat.

One of the main benefits of a bellows seal over a spring or dynamic 'O' ring type mechanical seal is that there is no auxiliary seal ring to hang up due to dirt or solids in pumpage or a faulty shaft. This eliminates the potential for fugitive emissions and allows for better barrier function and a higher overall fluid flow capacity.

There is also no risk of stick-slip' failure with a bellows seal, which can occur when a shaft or sleeve is installed improperly and does not have adequate space to support the weight of the seal. The design of a bellows mechanical seal also prevents vibration and runout from damaging the bellows assembly or the sleeve it is attached to.

Another advantage of a bellows seal is that the axially most part of the bellows stack assembly can fully compress without the radially most part of the drive end (40) coming into contact with it. This allows unwanted stress loading to be avoided, which in turn can extend the life of the seal and prevent premature mechanical seal failure.

This feature is not found in most dynamic 'O' ring type mechanical spring seals and is particularly advantageous for applications where the shaft or sleeve is subject to wear, or the pressure drop between the seal and the pump is high. Because the bellows stack assembly is a separate component, there are no other auxiliary seal rings to hang up and the overall service life of the seal is significantly extended.

The welded metal bellows have good floating and random compensation, which is useful in compensating for leakage caused by wear, axial movement, and vibration. The axial friction resistance of the welded metal bellows is reduced, allowing it to be used in more difficult conditions such as corrosive media, and at higher temperatures than spring-type seals.

As a result of these advantages, the welded metal bellows is a preferred option for many applications in the chemical industry and nuclear energy fields. However, there are some problems with the welded metal bellows. The initial elastic force range P of a welded metal bellows is relatively small, ranging from 556-708 N. This makes it hard for bellows to be fully displaced by the drive end (40) if the mechanical seal is designed to operate at low speeds.

It is important to consider the sizing of the welded metal bellows in the mechanical seal, as it should be selected such that the initial elastic force exceeds the maximum operating pressure of the mechanical seal. This is important to ensure that the bellows is not able to deflect or flex during operation.

TYS 10130 M37G Rubber bellow mechanical seal For Water Pump