of outside seal bands 70 whereas the inside cavity is formed between a pair of inside seal bands 72 the cavities 66 and 68 are functional voids in the invention design to distribute the pressure differential load on the seal substantially uniformly across the transverse plane of the seal pressure force vectors parallel with the wellbore axis although an accurate void shape 66 and 68 is illustrated as the preferred embodiment it will be understood that other void shapes such as a box or channel may be used to accommodate seal material movement due to pressure distortion and temperature expansion ideally the pressure differential load imposed on that seal band directly engaged with the highest pressure environment is distributed across the full annulus of the low pressure side of the seal whereby the unsupported ridge of low pressure sealing band carries only a fractional portion of the full pressure differential load dimensionally the o d of the outside seal bands 70 is greater than the o d of the end rims 56 similarly the i d of the inside seal bands 72 is less than the i d of the end rims 56 it is the outside seal bands 70 that make interface contact with the seal bore faces 38 on the outer assembly tube 22 it is the.