Abstract: Raw coal is fed into the upper end of an inclined internally scrolled barrel. Washed coal is screened after leaving the barrel, and the material passing the screen is divided into two batches, the coarser being returned to the barrel, the finer being separated into coal and waste by cyclone separators. The outputs of the separators are dewatered to provide liquor for effecting washing of raw coal in the barrel via a launder pipe, and to provide fluid for circulation from the screen to the separators.

Abstract: A sand settler filter with a weir and scum trough mounted on a tank having a valved sludge outlet, a perforate filter bed support carried below the weir and above an effluent feed to the tank is characterized by a pressure sensor responsive to a resistance to movement of contents of the tank and connected to a valved outlet from the tank, preferably through a ballast chamber operable, in a method according to the invention; for back flushing the filter bed and the valved sludge outlet preferably being operable in response to a torque sensor drivably coupled to a paddle carried at the bottom of the tank.