Double Shaft Seal

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

At first sight damage doesn’t look serious

When look closer we see the small craters

Even more spots than we expected

Small cracks connect the craters

Blistering is also known as dry-running in liquid bath. It happens because the lubrication oil contains a higher proportion refrigerant (liquid phase).  The refrigerant will be forced to go into gas phase because of the heat developed by the shaft seal: the heat of friction between the stationary- and rotating part.

The pressure of the refrigerant will lightly rise above the lubrication pressure and force out the lubrication film. The dry-running takes place. This phenomenon is known as blistering, dry-running in liquid bath or sometimes is called a corona effect.

This process also explains the short life span of bearing in refrigeration compressors.

The other causes of shaft failure

• Axial shaft movement out of limits (end play or thrust)
• Thermal shock of some seal face materials

• Radial shaft movement (run out or misalignment)
• Viscosity out of limits
• Centrifugal force out of design limits
• Pressure out of design limits
• Operation temperature out of design limits

If your shaft seal fails often contact us for the FREE consultation, please use our inspections form.