Answer:
In mobile hydraulics, those used in agricultural, industrial, and automotive applications a hydraulic accumulator works like a shock absorber for a hydraulic system. Often a hydraulic accumulator is composed of a housing with a diaphragm between the oil side and the gas side. Pressurized gas (usually dry nitrogen because of its low expansion/contraction properties in relationship to temperature). The accumulator will have a specification for the gas pressure and the hydraulic system can often be used to manipulate the pressure of the oil used in the accumulator depending upon a specific application.
Rapid increases and decreases for hydraulic power demands (most often occurring in open-center systems) can shock the hydraulic pump, lines and valves. Open-center positive-displacement systems (constantly providing hydraulic flow while the engine is running) must return to sump when there is no hydraulic need. This is done by use of a relief valve or a 'dump'-valve on the pressure side of the system. There are moments when the relief valve may have a very slight delay. This delay can cause the system to build pressure in a very short period of time and this can strain hydraulic components. So the accumulator it used to soften the blow just a little. Another example would be when using a float application with a hydraulic system, an accumulator may help to buffer the changing oil directions within the hydraulic system.