The sieve beds are filled with zeolite granules. Sieve beds should last at least 15,000 hours, and when regularly maintained even 20,000 hours or more.
Sieve beds tend to lose their filter properties over time. High humidity is often the reason. Water then condenses inside the filter and clogs the granules. Too high system pressure and low oxygen concentration is an indicator for a blocked filter. You will also get asymmetric concentration measurement results because one sieve tank will deliver more oxygen than the others as the control circuit periodically switches between them.
A clogged sieve that contains water also weighs more, which leads that the oxygen purity decreasing, sieves have to be exchanged. Please note, that sieves should always be replaced in pairs, even when only one is a defect.
In principle it is easy to prevent moisture in the sieve beds – the concentrator just has to run regularly. Concentrators that are not in use should be switched on for at least half an hour every week, in regions with high humidity maybe twice a week.