Piston accumulators use pistons as separating elements. They can handle much higher gas compression ratios (up to 10:1) and flow rates as high as 215 litres (57 gallons) per second. However, the piston inside the accumulator causes internal friction that negatively affects reaction speed (i.e. has slower response times greater than 25 ms).

Piston accumulators also require a higher level of fluid cleanliness than bladder units. Piston accumulators are used for very large fluid storage requirements of up to 2,500 litres at very high pressures (up to 1,000 bar).