(under subclass 345) Devices having vertical water tubes in the rear of the bridge wall and communicating with a longitudinal upper and a longitudinal lower drum. There may or may not be water tubes above the firebox, but the products of combustion do not return.
SEE OR SEARCH THIS CLASS, SUBCLASS:
346, for vertical water tube boilers having horizontal longitudinal upper and lower drums where the products of combustion pass also rearwardly through the tubes.
444, for miscellaneous combinations of means for heating the feed water in a water tube boiler either outside or inside the water space of the boiler.
