Pneumatic actuators used in devices that, by their function require light weight and small size such as orthotics, can benefit from the inclusion of accumulators to harness and recycle energy normally lost in exhausted gases. In order for an accumulator to provide benefits to these small systems, they must possess relatively high gravimetric and volumetric energy densities with adequately high efficiencies as compared to conventional accumulators, like traditional spring piston accumulators. Constructing accumulators that primarily use strain as the primary energy storage method can provide the energy storage capacities and efficiencies needed, as well as a better pressure-volume relationship than a fixed-volume accumulator. This paper outlines the behavior of an elastomeric strain accumulator constructed using natural rubber tubes as the material for an accumulator. Tube shaped accumulators fill to a preset maximum diameter, constrained by a rigid shroud so that the material’s yield strength is not approached and to control the manner in which the accumulator expands. Controlling the manner of expansion for the accumulator allows a relatively constant pressure to be used through the majority of the fill cycle. Natural rubber accumulators were experimentally evaluated and characterized for their energy storage efficiencies over a range of different parameters allowing basic design criteria to be created for use in building accumulators tailored to specific system requirements.

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