+------------+----------------+---------------+ |Size of unit|Babcock & Wilcox| H. R. T. | |Horse Power |Feet and Inches |Feet and Inches| +------------+----------------+---------------+ | 100 | 7 3 × 19 9 | 10 0 × 20 0 | | 150 | 7 10 × 19 9 | 10 0 × 22 6 | | 200 | 9 0 × 19 9 | 11 6 × 23 10 | | 250 | 9 0 × 19 9 | 11 6 × 23 10 | | 300 | 10 2 × 19 9 | 12 0 × 25 0 | +------------+----------------+---------------+ BABCOCK & WILCOX BOILERS AS COMPARED WITH OTHER WATER-TUBE DESIGNS It must be borne in mind that the simple fact that a boiler is of the water-tube design does not as a necessity indicate that it is a good or safe boiler. Safety--Many of the water-tube boilers on the market are as lacking as are fire-tube boilers in the positive circulation which, as has been demonstrated by Mr. Babcock's lecture, is so necessary in the requirements of the perfect steam boiler. In boilers using water-leg construction, there is danger of defective circulation, leaks are common, and unsuspected corrosion may be going on in portions of the boiler that cannot be inspected. Stresses due to unequal expansion of the metal cannot be well avoided but they may be minimized by maintaining at the same temperature all pressure parts of the boiler. The result is to be secured only by means of a well defined circulation. The main feature to which the Babcock & Wilcox boiler owes its safety is the construction made possible by the use of headers, by which the water in each vertical row of tubes is separated from that in the adjacent rows. This construction results in the very efficient circulation produced through the breaking up of the steam and water in the front headers, the effect of these headers in producing such a positive circulation having been clearly demonstrated in Mr. Babcock's lecture. The use of a number of sections, thus composed of headers and tubes, has a distinct advantage over the use of a common chamber at the outlet ends of the tubes. In the former case the circulation of water in one vertical row of tubes cannot interfere with that in the other rows, while in the latter construction there will be downward as well as upward currents and such downward currents tend to neutralize any good effect there might be through the diminution of the density of the water column by the steam. Further, the circulation results directly from the design of the boiler and requires no assistance from "retarders", check valves and the like, within the boiler. All such mechanical devices in the interior of a boiler serve only to complicate the design and should not be used. This positive and efficient circulation assures that all portions of the pressure parts of the Babcock & Wilcox boiler will be at approximately the same temperature and in this way strains resulting from unequal temperatures are obviated.