Accumulators are storage vessels that hold fluid under pressure as energy to be released on demand, and are commonly used in fluid power systems to improve performance. When used in hydraulic circuits and machinery, they are sometimes referred to as hydraulic accumulators or hydropneumatic accumulators. Accumulators are also used to eliminate pulsations for a smooth fluid flow and protect systems from hydraulic shock or water hammer. The most common design has an internal bladder that separates stored process fluid from a compressed gas charge.