Hydraulic Accumulator

Hydraulic Accumulator - Inside, a moveable or flexible barrier—usually a piston or rubber bladder—separates the oil from the gas. Analogous to rechargeable batteries in electrical systems, they store and discharge energy in the form of pressurized fluid and are often used to improve hydraulic-system efficiency.
An accumulator itself is a pressure vessel that holds hydraulic fluid and a compressible gas, typically nitrogen. The housing or shell is made of materials like steel, stainless steel, aluminum, titanium and fiber-reinforced composites. Hydraulic accumulators are energy storage devices.