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.
- 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.