Seals under pressure
When a seal is exposed to pressure, the radial load of the sealing lip increases. This in turn increases the actual sealing lip/shaft contact area, resulting in additional friction and elevated underlip temperatures. Therefore, the guideline values for speeds provided in the diagram 1 do not apply.
The diagram 2 shows an example of lip distortion of a conventional sealing lip design as sump pressure increases, resulting in reduced seal service life.
SKF CRW5 and CRWA5 pressure profile seals (fig 1) are designed to withstand pressure differentials of 0,34 MPa (50 psi) at speeds up to 5 m/s (1 000 ft/min).
When there is a pressure differential across the seal, a shoulder or retaining ring should be used at the low-pressure side of the seal to prevent it from being pressed out of the housing bore (fig 2).