Gas permeation is the penetration of a gas (i.e. Nitrogen) through a solid. With regards to accumulators, this is the permeation of the gas though the bladder or membrane (diaphragm). In general, the industry standard for gas loss (permeation rate) for bladders and diaphragms is ~10% per year. However, HYDAC’s permeation rates are typically better meaning less times that you have to add gas to the accumulator in order to maintain the precharge pressure.