Title: Silencing a Noisy Agitator Seal By Managing Stress

Abstract: Did you know the sound that comes when you run your finger on the rim of a wine glass is referred to as "partial boundary layer lubrication"? Did you know this same phenomenon also occurs commonly on buffer and media tank agitators in bio-processing facilities? However, on agitator seals the sound can amplify to over 90 decibels, which exceeds OSHA’s personal exposure limits.

Using an FEA model, John Crane found, that the noise from partial boundary layer lubrication is a result of vibration caused by the application of an even or consistent stress to the seal face, which is consistent with field trials since the seals rarely squealed at startup. Instead, the seals squeal after some run time when the right amount of stress is applied. This stress could come from the pressure of the vapor space in the tank or vessel, which also explains why the noise level and pitch can come and go depending on the pressure in the tank, agitator speed, as well as other scenarios.

This led to the discovery that the squealing can be reduced, or even eliminated, by managing the stress imposed on the agitator seal faces. Subsequently, John Crane developed a solution that results in an active seal face, meaning the degrees of flatness change with the stresses applied during operation. In other words, the rim of the wine glass changes as you run your finger around it preventing the noise condition from ever taking place.

Take Home Message from Poster: The noise from a media or buffer tank agitator seal can be reduced, making a quieter and safer workspace.