The service life of the filters in TOR-5 is not defined by calendar time alone, but mainly by the amount of moisture they actually adsorb and the number of regeneration cycles. In stable mid-life transformers, a single cartridge set can typically operate for several months before regeneration is required. With proper regeneration, the same zeolite can be reused many times, so the practical lifetime is often several years. What really limits life is oil contamination and mechanical degradation, not simple saturation.