Description
Class F22D : PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER; FEED-WATER SUPPLY; CONTROLLING WATER LEVEL; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN BOILERS
Subclass 1/10: Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) the tubes having fins, ribs, gills, corrugations, or the like on their outer surfaces, e.g. in vertical arrangement in horizontal arrangement (hollow fire-bars, grates, or the like used as water tubes F23H 3/02)