Abstract: The operating performance and reliability of a pump, e.g. a hydraulic pump, can be significantly improved by incorporating an actively controlled positive displacement control valve in fluid communication with a fixed displacement pump, supply fluid line, and return fluid line. In use, the pump may be used to move fluid from the suction side to the discharge side of the pump, including fully opening the suction circuit to the pump cylinder and fully closing the pump discharge circuit during a pump suction stroke, fully closing the suction circuit and fully opening the pump discharge circuit to a downstream circuit during a pump discharge stroke, and allowing fluid to be pumped without the fluid passing through a valve spring loaded check valve.

Abstract: A hydraulic accumulator for subsea use, which charges itself as it is lowered to the operating depth. The seawater and hydraulic fluid operate against unbalanced pistons (36, 52) with low pressure gas (42) therebetween.