How a gravity-fed rotary drum filter works
An interactive model of a gravity-fed rotary drum filter, built by Play It Koi.
The failure modes are in here too, including the one where a filter set too low for its pond quietly runs water out the waste line while the auto-fill valve pays for it. Move the controls and watch what the water does.
Comparing the two feed styles? The pump-fed version is here.
With the pump off, the water inside the filter sits level with the pond. Start the pump and it draws from the clean side, pulling that level down. The gap it opens is what pushes water through the drum screen, carrying it from the dirty side into the clean side. Everything else is bolted to the housing, so where the pond sits decides how the whole thing behaves.
About this model. Proportions are generic rather than any one manufacturer's unit, and time runs faster than real life so a wash cycle and an overflow are both watchable. Drum size, drawdown and wash water use vary widely from one unit and one pond to the next, so this shows how the parts behave rather than what any particular filter will do.