Hybrid shaft seal assembly for movable shafts

A fluid consumer comprising:

• a housing for containing an operating fluid;
• a shaft movable relative to the housing;
• and
• a shaft seal assembly configured to seal against a mating surface of the shaft to restrict leakage from a fluid-side of the consumer, the shaft seal assembly comprising:
• a seal case movable relative to the mating surface of the shaft;
• a biasing force that biases the seal case towards the mating surface of the shaft;
• and
• a seal at least partially disposed in the seal case, the seal being configured to seal against the mating surface of the shaft;
• wherein the consumer is configured such that:
• when in use, fluid pressure from the fluid-side exerts a fluid force against the seal case that is opposite the biasing force,
• when fluid pressure exerted against the seal case is equal to or greater than a threshold pressure, (i) the fluid force against the seal case overcomes the biasing force such that the seal case sealingly separates from mating surface of the shaft, and (ii) the fluid pressure from the fluid-side also exerts a force against the seal that forces the seal into sealing engagement against the mating surface of the shaft to form a dynamic seal;
• and
• when fluid pressure exerted against the seal case is less than the threshold pressure, (i) the seal is sealingly engaged against the mating surface of the shaft to form a static seal, and (ii) the biasing force overcomes the fluid force against the seal case, such that a sealing surface of the seal case is sealingly engaged against the mating surface of the shaft to form an additional static seal.