B,  Centrifugal Pump,  Seals & Flush Plans

Balance Ratio (Mechanical Seals)

The ratio (B) of the hydraulically loaded surface area (Ah) to the sliding surface area (As) of a mechanical seal face. A 70/30 balance ratio means 70% of the seal face closing area experiences the stuffing box pressure and 30% does not. In this example, the balance ratio, B, is 0.7.

By definition:

  • Balanced mechanical seals have a balance ratio B<1
  • Unbalanced mechanical seals have a balance ratio B>1
  • The balance ratio is often designed to run between 0.6 and 0.8

Lower balance ratios result in a thicker lubricating films and higher leak rates. The choice of the balance ratio is a compromise between lower heat generation, leak rates, and stability of the sealing gap.


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