Hydraulic accumulators are a pressure vessel to store energy in. There are several different designs possible including bladder, spring, metal disk and piston. We have chosen to develop a piston type with an external gas bottle. This type of accumulator uses compressed nitrogen for energy storage.

One design challenge with bladder or piston accumulators is gas permeability of the material between the nitrogen and the oil. Nitrogen will penetrate all elastomeric materials but some are more resistant than others. A piston type accumulator only has to seal gas between the piston and the barrel so the amount of elastomeric material subjected to the nitrogen is reduced. Design problems of piston type accumulators are, the piston seal is subjected to sliding against the barrel, the barrel diameter increases with pressure and the seal material must be able to handle the working and spike pressures the system will see.

To address these problems we will be applying our StepLock piston ring with a Hydrin expander. Hydrin has the lowest permeation rate of all rubber like materials and the piston ring will be made from acetal. By separating the gas storage from the hydraulic fluid area there will be weight savings as the gas bottle can be a composite over wrapped pressure vessel instead of all steel construction.

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