The bag is filled with nitrogen at precharge pressure Po through the precharge valve. In the ASL type separator accumulator, the liquid also exists in the pocket.

The AST transfer accumulator is designed for the connection of nitrogen cylinders. The diffusion tube prevents damage to the bag while the accumulator is working. Nitrogen cylinders are used as back-up to increase the volume of gas in the accumulator. This means that a small accumulator can use a lot of gas, so costs can be reduced.

When the liquid enters the accumulator and the pressure exceeds the precharge pressure, the liquid begins to build up inside and the nitrogen pressure begins to rise parallel to the fluid pressure. The volume of the gas is reduced to make room for the pressurized liquid. When the liquid side pressure falls below the gas pressure value, the accumulator begins to distribute the accumulated fluid. When the accumulator is empty, or in any case when the liquid pressure is lower than the gas pressure, the lift valve of the liquid valve is closed to prevent the bag from squeezing and breaking.