Sealing apparatus having sequentially engageable seals

Advantageous seal systems are provided that include a barrier member movable relative to a shaft to allow sequential engagement of resilient seal members, e.g., lip seals, with the shaft. Movement of the barrier member may be effected manually or through introduction of pressurized fluid to effect piston-like movement. The disclosed seal assemblies may include an automatic leak detector and may utilize such leak detection to effectuate automatic movement of the barrier member. The barrier member may be moved relative to the shaft while the shaft is in movement, e.g., rotating or reciprocating, thereby permitting seal maintenance without interruption in operation. As seal members are sequentially brought into sealing engagement with the shaft, the previously engaged seal members contribute to the sealing performance of the seal assembly, although no longer effective to establish a stand-alone seal with the shaft.