Patent ID: 7424917

Claim:
A subsea system comprising a pump system for providing operational power fluid to a subsea device for operating the subsea device, a compensated pressure reservoir system for receiving operational power fluid from the subsea device and for providing operational power fluid to the pump system, the compensated pressure reservoir system comprising a body with an interior chamber, a first opening in the body, and a second opening in the body, an amount of operational hydraulic fluid in the interior chamber under a first pressure, a piston movably and sealingly mounted in the interior chamber, the piston closing off the first opening and preventing hydraulic fluid from exiting through the first opening from the interior chamber, the piston having an outer surface and an inner surface, the operational hydraulic fluid applying the first pressure against the piston's inner surface, fluid exterior to the pressure compensated reservoir able to apply pressure to the outer surface of the piston, a piston rod with a first end and a second end, the first end connected to the interior surface of the piston, the second end projecting through the second opening, a piston rod chamber having an interior, the second end of the piston rod projecting into and movable in the piston rod chamber, at least one operating channel through the body for providing hydraulic fluid from the reservoir for operating an hydraulically-powered apparatus, a fluid system for providing fluid under pressure to the second piston rod end within the piston rod chamber, a channel through the piston rod chamber, the fluid system in fluid communication with the interior of the piston rod chamber via the channel, the outer surface of the piston greater than the inner surface of the piston and the outer surface positioned for pressure thereagainst by the fluid exterior to the body creating a pressure differential between the first pressure of the operational hydraulic fluid and pressure applied by the fluid exterior to the body, and the pressure of the fluid of the fluid system compensating for the pressure differential.