My iAVs went for 7 years, no maintenance or sand replacement. I speak with people who have had systems going for over 13 years, consistently. Gordon Watkins had his iAVs running for 22 years. My teacher knows a family that has had it in their family for over 30 years.
Good video at
https://www.youtube.com/watch?v=LNZzpbvEMNI
