Description
Class F22D : PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER; FEED-WATER SUPPLY; CONTROLLING WATER LEVEL; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN BOILERS
Subclass 1/04: 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 plain outer surfaces, e.g. in vertical arrangement