Modern Gasworks Practice

370 MODERN GASWORKS PRACTICE The coal to be waslied is elevated from the slurry tank into a revolving screen which separates the wet coal into sizes from T3T inch to 0. The oversize passes into a separate washing compartment, and the undersize is only what passes through, a t-Jö mesh, which averages about 2 per cent. This revolving screen is partially immersed in water which enables the finest sizes to be treated without clogging. The various Fics. 258.—The Coptée Coal Washer. sizes pass through water-sealed revolving star delivery valves, aad through the feeder launclers into the washer, where they meet an upward current of water regu-lated in velocity so as to float the lighter coal particles, and at the same time allow the heavier particles of shale to fall. This is accomplislied by a very simple device, consisting of an inverted plain or perforated cone attached to a straight length of