Self-venting seal assembly

A low pressure seal is used to energize a high-pressure seal, the low-pressure seal having a "u" shaped cross-section, thereby creating a groove in a first end of the low-pressure seal. When the first end of the seal is exposed to pressurized fluid, it expands outwardly thereby preventing the leakage of fluid past it. To the extent that any pressurized fluid does leak past the seal, which would act against a second end of the seal when the pressure on the opposite side of the seal drops, the seal compresses inwardly, thereby allowing the pressurized fluid to flow back past the seal. The high-pressure seal comprises a sleeve seal having an annular opening through which the plunger reciprocates, the sleeve seal being supported by a backup ring. The backup ring also has an annular opening through which the plunger passes. The sleeve seal and backup ring are configured such that they may be placed in an annular bore of a seal carrier and an annular end surface of the sleeve seal and an annular surface of the backup ring abut each other and are substantially flush.