Abstract: An actuation installation for use under extreme environmental conditions, such as freezing, uses a two-fluid system in which one fluid is impervious to the extreme environment, and the other fluid, such as water, is not. A two-chamber accumulator-separator has a water chamber connected to a water source via control valves and a working fluid chamber connected to a hydraulic actuator port. The other actuator port is connected to a working fluid chamber of a two-chamber accumulator having a sealed air-pressure chamber. When water is admitted to the water chamber, the actuator will move in a first direction further compressing the air in the air pressure chamber. When the water is drained from the water chamber, the accumulator air-pressure moves the actuator in the opposite direction. The actuator is positioned in the extreme environment, with the remainder of the system installed in a protected environment such as underground.