The utility model discloses a closed filter, it mainly comprises bottom plate, cylinder, filter plate, filter cloth, filter cloth clamp plate, elliptic type head, quick -opening manhole, set up the feed liquor pipe on the elliptic type head, advance compressed air pipe, advance the hot -water line, observe the sight glass, the cylinder sets up quick -opening manhole to can clear away filter residue and clear filter wash cloth during the operation fast, the cylinder bottom sets up the drain pipe to to filtrate and in time discharge, the filter cloth tiling is on the filter plate, and the filter cloth is peripheral presses with the filter cloth clamp plate, and the reuse screw bolt and nut is turned round tightly, compresses tightly the filter cloth, the closed filter shell adopts insulation material to keep warm to prevent solution crystallized blocking filter cloth in filter process, the utility model discloses closed filter filtering pressure is high, and the filter effect is good, and the filter residue is easily cleared up, and the filter cloth easily washs, and thermal insulation performance is good moreover, and difficult production is cooled off the crystallization and is blockked up the filter cloth among the filter process.