An apparatus including: - an accumulator including: ∘ an energy storage apparatus with a movable first piston face , the movable first piston face configured to reversibly compress an energy storage medium; ∘ a movable second piston face forming at least part of an inner surface of a corresponding second fluid chamber reversibly expandable by said second piston face ; ∘ a movable third piston face forming at least part of an inner surface of a corresponding third fluid chamber reversibly expandable by said third piston face ; wherein said first, second and third piston faces are coupled together; - a reciprocating component ; - a prime mover ; - a drive mechanism capable of moving the reciprocating component reciprocally and/or cyclically, said drive mechanism including a hydraulic drive motor ; - hydraulic fluid interconnections with a combination of hydraulic lines including at least one: ∘ pressure line from the prime mover to: • the drive motor ; • accumulator second fluid chamber ; • accumulator third fluid chamber ; ∘ drain line input to the prime mover from: • the drive motor ; • accumulator second fluid chamber ; ∘ pressure line from the accumulator third fluid chamber to: • the drive motor ; wherein the accumulator further includes fluid conduits, valves and/or connections configured to concurrently: input hydraulic fluid to the second fluid chamber , and output hydraulic fluid from the third fluid chamber to the drive motor . - an accumulator including: ∘ an energy storage apparatus with a movable first piston face , the movable first piston face configured to reversibly compress an energy storage medium; ∘ a movable second piston face forming at least part of an inner surface of a corresponding second fluid chamber reversibly expandable by said second piston face ; ∘ a movable third piston face forming at least part of an inner surface of a corresponding third fluid chamber reversibly expandable by said third piston face ; wherein said first, second and third piston faces are coupled together; ∘ an energy storage apparatus with a movable first piston face , the movable first piston face configured to reversibly compress an energy storage medium; ∘ a movable second piston face forming at least part of an inner surface of a corresponding second fluid chamber reversibly expandable by said second piston face ; ∘ a movable third piston face forming at least part of an inner surface of a corresponding third fluid chamber reversibly expandable by said third piston face ; - a reciprocating component ; - a prime mover ; - a drive mechanism capable of moving the reciprocating component reciprocally and/or cyclically, said drive mechanism including a hydraulic drive motor ; - hydraulic fluid interconnections with a combination of hydraulic lines including at least one: ∘ pressure line from the prime mover to: • the drive motor ; • accumulator second fluid chamber ; • accumulator third fluid chamber ; ∘ drain line input to the prime mover from: • the drive motor ; • accumulator second fluid chamber ; ∘ pressure line from the accumulator third fluid chamber to: • the drive motor ; ∘ pressure line from the prime mover to: • the drive motor ; • accumulator second fluid chamber ; • accumulator third fluid chamber ; • the drive motor ; • accumulator second fluid chamber ; • accumulator third fluid chamber ; ∘ drain line input to the prime mover from: • the drive motor ; • accumulator second fluid chamber ; • the drive motor ; • accumulator second fluid chamber ; ∘ pressure line from the accumulator third fluid chamber to: • the drive motor ; input hydraulic fluid to the second fluid chamber , and output hydraulic fluid from the third fluid chamber to the drive motor . <EOS>