Which device stores energy by compressing gas?

• A. Reservoir
• B. Filters
• C. Manometer
• D. Accumulator (correct)

Answer: (D)

Energy storage in hydraulic systems is achieved by compressing gas inside a device called an accumulator. This sealed vessel holds a gas chamber separated from the hydraulic fluid by a bladder, piston, or diaphragm. When system pressure rises, fluid enters the accumulator and compresses the gas, storing energy as pressure energy. When demand spikes or pressure drops, the compressed gas expands, pushing fluid back into the system to maintain pressure and supply extra flow. This makes accumulators especially useful for smoothing pressure, absorbing shocks, and providing short-term power during peak needs.

Other components don’t store energy in this way: a reservoir mainly holds extra fluid volume, a filter cleans fluid, and a manometer measures pressure. None of these store energy by compressing gas.