Double 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. This condition will lead to shaft seal failure.

At first glance, damage doesn’t look serious

When we look closer we see small craters

Even more spots than we expected

Small cracks connect the craters

Blistering is also known as dry-running in liquid bath, or the corona efect. It occurs because the lubrication oil contains a higher proportion of refrigerant (in the liquid phase). Friction between the stationary and rotating seal parts forces the refrigerant to evaporate into gas.

The pressure of the refrigerant will rise slightly above the lubrication pressure and force out the lubrication film, resulting in dry running.

This phenomenon also explains the short lifespan of bearing in refrigeration compressors.

Other causes of shaft failure

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

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

If your shaft seal fails often, contact us for a FREE consultation using our inspections form.