In the metal bellows mechanical seal, a bellows made of welded lamellae welded o corrugated replaces the springs, performing the function ofmechanical loading on the sealing surfaces e allowing to tolerate shaft movements while keeping the secondary seal static.
This advantage makes the metal bellows seal suitable for applications where the maintenance of elasticity of the secondary seal, cannot be guaranteed, such as in high-temperature applications. Indeed, in the metal bellows seal, the secondary seal is completely static but suitable for working with very high temperatures e the elasticity needed to follow the micro-movements of the shaft is guaranteed by the metal bellows.
For this reason, the API682 standard distinguishes between seals with springs and “O-rings that are dynamic” defining them “pusher”, and those with metal bellows defined “bellows”. The bellows seals, are suggested for applications above 176°C.