Under the action of pressure, the volume change of the liquid (under the condition of constant temperature) is very small, so if there is no power source (that is, the supplement of high-pressure liquid), the pressure of the liquid will drop rapidly.
The elasticity of gas is much greater, because gas is compressible, and it is still possible to maintain a relatively high pressure in the case of a large volume change. Therefore, when the accumulator is replenishing the hydraulic oil of the hydraulic system, when the volume of the liquid has changed, the high-pressure gas can continue to maintain the pressure of the hydraulic oil, so that the volume of the hydraulic oil in the container will not decrease due to the replenishment of the hydraulic oil. becomes smaller, resulting in a rapid loss of pressure of the hydraulic oil.
As for nitrogen, the main reason is that nitrogen is stable in nature and does not have oxidation or reduction properties, which is very good for maintaining the performance of hydraulic oil, and will not cause oxidation/reduction denaturation of hydraulic oil!
Nitrogen is the pre-charging pressure and is installed in the air bag of the accumulator, which is separated from the hydraulic oil! When you fill the accumulator with hydraulic oil, due to the pressure of the nitrogen air bag on the hydraulic oil, that is, the pressure of the hydraulic oil is equal to the pressure of nitrogen gas. As the hydraulic oil rushes in, the nitrogen air bag is compressed, the pressure of nitrogen gas increases, and the hydraulic pressure increases. The pressure of the oil increases accordingly until the hydraulic oil is filled to the set pressure!
The function of the accumulator is to provide a certain pressure of hydraulic oil, which is generated by the force of nitrogen!