Vibrations can arise in mechanical seals as axial vibrations, radial vibrations and torsional vibrations. As a rule, these vibrations are forced vibrations in the subcritical range, often with superimposition. Causes of axial vibrations in pumps are a) pressure fluctuations, with transfer of vibrations to the mechanical seals by way of the rotor and shaft or the housing; b) pulsating vaporization in the sealing gap. These axial vibrations give rise to derangement of the sliding faces to thermal overloading of secondary seal elements due to churning, and to spring fracture as the result of material fatigue. Axial vibrations in a metal bellows seal can shorten the life of the metal bellows considerably. For this reason, the ambient frequency must never equal the natural frequency of the bellows. If the ambient frequency is known, the bellows can be designed with a natural frequency outside the critical frequency range.

The natural frequency of the bellows is varied by changing the spring characteristic and the mass. Radial vibrations are caused by shaft deflection or unbalance, but they can also be excited in mechanical seals by friction between the sliding faces. Radial vibrations produce a high rate of wear on face materials, combined with an increase of temperature in the area of the sliding faces. Superimposition of axial and radial vibrations results from run-out errors and produces wobbling. Torsional vibrations are caused in mechanical seals by changes to the conditions of friction in the sealing gap. Alternating torsional stresses in bellows seals can damage the bellows as well as the sliding faces.