Automatic arrangements for opening and shutting the valves of a sewage filter are only to be trusted where a small quantity of sewage is to be dealt with. Fig. 1 illustrates a mode of filling and emptying two filters automatically by means of tippers connected by bell-cranks to the trough which brings down the liquid to be filtered. Filter A, on the right, is supposed to be filled up to the level of the overflow, when the liquid, escaping into the tipper, pulls down the bell-crank, and pushes over the sewage trough to such a position that the flow of sewage is diverted into filter B. At the same time the outlet valve of filter A is opened by means of the wire attached to the top of the bell-crank. The supply trough is pivoted at one end, and is carried at the other end on a roller, so as to move easily: the arrangement is shown in Fig. 2. Instead of having a movable trough, the arrangement shown in Fig. 3 may be used, where a movable division can be turned over so as to divert the liquid into either channel as required. Fig. 4 is a well-known form of tipper for discharging alternately to the right or left, but with this both filters would be worked at the same time, instead of alternately, as in the first arrangement.

Automatic Sewage Filter.