A hydro-pneumatic piston accumulator is a device used specifically for storage of liquid under pressure. As liquids, for all practical purposes, are incompressible, this objective is achieved by utilizing the compressibility of gases. A floating piston is fitted into the accumulator tube. An inert gas - nitrogen - is filled into the gas side through a pressure valve to a pressure. The piston moves to the bottom end, filling the entire volume of the accumulator. When the system pressure is higher than the gas precharge pressure, the liquid enters the accumulator and the piston is moved towards the gas side compressing and reducing the gas volume. Should the liquid pressure rise, the volume of gas reduces with an attendant rise in pressure, thus balancing the Liquid pressure. A potential energy is now stored in the accumulator to be utilized whenever needed.