Depending on the mode of operation, hydraulic accumulators are based on the principle of bubble and membrane accumulators or liquid sound dampers. In hydropneumatic dampers, the compressibility of a gas (mostly nitrogen) is used for damping. In the case of a bladder accumulator, for example, the bladder is compressed or expanded as a function of the magnitude of the variations in pressure. A similar behavior is exhibited by membrane accumulators as well. Specifically, hydropneumatic dampers (pulse-tone pulsation dampers) were developed because damping may be impaired because of disadvantageous connection of the hydraulic fluid to the volume of gas when standard bladder or membrane accumulators are used. Dampers of this type have an in-line connecting block by means of which the variations in volume or pressure are optimally coupled to the gas volume. Good damping properties up to a frequency of around 500 Hz can be obtained with these dampers (see Mannesmann-Rexroth design projects “Konstruktion von Hydroanlagen” (Construction of Hydraulic Facilities), Der Hydrauliktrainer, Vol. 3, 1st Edition, page 106).
In conventional solutions readily available commercially, a connecting point is provided in the accumulator housing to increase the gas supply volume by mounting on the gas supply side an accumulator cylinder in which the additional operating gas, in particular in the form of nitrogen, is stored. Such solutions are costly in manufacture, and are geometrically large. Sealing problems may arise at the connecting point in question, leading to loss of operating gas. To improve the solutions, it has already been proposed that the gas supply chamber in the accumulator housing itself be enlarged and that additional supply cylinders connected to the accumulator housing be eliminated. However, enlargement of the gas supply chamber in the accumulator housing also increases free, travel for the separating element or separating membrane, so that it is subjected to heavy wear, such as by folding and overstretching processes, so that failure of the accumulator device soon ensues.
The solutions, discussed in the foregoing with the accumulator cylinder of operating gas mounted on the device, allow reduction of the clear path of displacement inside the accumulator housing for the separating element. However, on the whole, the operating capacity of the accumulator is adversely affected, especially with respect to pulsation damping.
In addition, the conventional solutions have separating elements of an elastomer material which are essentially gas-permeable to a certain extent. Loss of gas due to diffusion and permeation processes occurs in the long term. The gas supply is transferred to the fluid side.