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MODERN STEAM PRACTICE.
the stays being regulated by the steam pressure used. For strength-ening the flues when they are of extra size sometimes angle-ironand manufactured hoops are introduced at the joints(see sketch on page 26). This plan answers wellwhere deposits do not form rapidly; and althoughlarge flues, whether oval or circular, are not at alldesirable, they can be strongly stayed with conicaltubes, having the water inside of the tubes, which are most efficientstays, and give extra heating surface, and no boiler having large orflat flues should be without such a means of Support. The tube-
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Fig. 44.—Flat IronFlue Ring.
stays are so made that the bottom parts with flanges can go throughthe top holes; thus they can be fitted to existing boilers cheaply.Such a System of staying must tend to decrease the number of
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boiler explosions; but on no account should a boiler so fitted betampered with. For staying the end-plates of round boilersT-irons are sometimes introduced, having long rods of round ironpassing from end to end of the boiler, and jointed with pins and