The service life of the TOR-5 filter cartridges is not fixed by time, but mainly by oil cleanliness, particle load, and operating conditions. In stable transformers with clean oil, cartridges can often operate several months to a year before replacement. Their role is primarily to protect pumps and sensors, not deep purification. In dusty environments or after oil treatment, clogging can occur faster, so differential pressure and flow are better indicators of end of life than calendar time.