How does an accumulator work?

A hydro-pneumatic accumulator stores hydraulic energy in a manner similar to how a car battery stores electrical energy. It is a pressure vessel that is comprised of a membrane or piston that contains a pressurized inert gas (typically nitrogen) and is connected to a fluid system. The gas pressure of the nitrogen is called the ''precharge pressure''. As the system pressure exceeds the precharge pressure, the nitrogen gas will begin to compress and decrease in volume allowing fluid to enter the accumulator. As the fluid system reaches its maximum pressure, the maximum amount of fluid will be contained inside the accumulator for a given pressure range and the nitrogen gas is compressed to the smallest possible gas volume. The accumulator is now able to supply fluid to the hydraulic system allowing it to do work. This is accomplished by the system pressure decreasing which, in turn, causes the nitrogen gas to expand displacing fluid from the accumulator into the hydraulic system under pressure.