The hydropneumatic accumulator allows a considerable accumulation of energy within confined spaces in hydraulic circuits. As liquids are practically incompressible and not therefore suitable for energy accumulation, such purpose is achieved by making use of the high compressibility of gases.
In practice a pressure vessel is used containing a separator diaphragm, as flexible barrier between the hydraulic fluid and the nitrogen gas. Through an inflating valve the inert gas, at a present pressure (Po), is indroduced into the diaphragm. Connection to the hydraulic circuit is located on the side opposite to the gas-fill valve.
When the circuit pressure exceeds the precharging pressure Po, the liquid enters the accumulator thereby compressing the diaphragm until the two pressures (liquid-gas) are equal. In this way is obtained a certain store of liquid under pressure, i.e. a reserve of potential energy which can be used for a lot of different applications.