15
november
2010

BLISTERING damage and the shaft seal

The most common reason for shaft seal failure is blistering. Blisters form unexpectedly and degrade the surface of the seal face, causing irregularities in the  running area and resulting in poor performance -- higher leak rates and higher friction -- causing failure of the shaft seal.

blistering-shaftseal

Blistering is also known as dry-running in a liquid bath, or the corona effect. It occurs because the lubrication oil contains a higher proportion of refrigerant (liquid phase).  This forces the refrigerant into the gas phase because of the heat developed by the shaft seal: the heat  friction between the stationary and rotating part.

The pressure of the refrigerant will rise slightly above the lubrication pressure and force out the lubrication film, causing dry-running. This phenomenon also explains the short life span of bearings in refrigeration compressors.