Abstract: The rotating backwash isolation hood of a multibed filter is raised and lowered by either hydraulic forces and gravity, or by an improved mechanism employing a pair of pistons and cylinders and a perforated indexing disc, or by both of these arrangements. The force required to lift the hood is reduced by eliminating the effect of the static head of the liquid above the hood. Leakage between the hood and the filter it covers is detected by a pressure differential indicating switch. A floculator may be combined with the multibed filter, and the dirty backwash liquid from the hood may be recirculated into the floculator.