Distinguish between an accumulator and a simple pressure vessel in hydraulic systems.

• A. An accumulator stores energy and dampens pressure fluctuations; a pressure vessel simply holds hydraulic fluid at a given pressure
• B. A pressure vessel stores energy; an accumulator is a simple container
• C. Both are the same; no difference
• D. An accumulator converts energy to mechanical work

Answer: (A)

In hydraulic systems the essential difference is energy storage versus simple containment. An accumulator stores energy by compressing a gas (or moving a piston/diaphragm) with hydraulic fluid; this stored energy can be released quickly to meet peak demands or to smooth out pressure surges, acting as a cushion for the system. A simple pressure vessel, by contrast, is just a pressure-rated container that holds fluid at a given pressure—its job is to contain fluid, not to store energy for rapid release or to dampen fluctuations. If you see a gas-precharged chamber or a movable piston/diaphragm inside the device, you’re looking at an energy-storage accumulator; if you only see a tank-like container with no mechanism for energy release, it’s a pressure vessel.