Steam:
Its Generation and Use

•* 8.—Dryness of Steam. The large disengaging surface of the water in the drum, together with the fact that the steam is delivered at one end and taken out at the other, secures a thorough separation of the steam from the water, even when the boiler is forced to its utmost. Most tubular, locomotive and sectional boilers make wet steam, “priming” or “foam- ing,” as it is called, and in many “super-heating surface” is provided to “dry the steam;” but such surface is always a source of trouble, and is incapable of being graduated to the varying re- quirements of the steam. No part of a boiler not exposed to water on the one side should be sub- jected to the heat of the fire upon the other, as the is so far reduced that if overheating should occur no explosion could result. 12.—Capacity. This is a point of the greatest importance, and upon it depends, in a large measure, the satisfac- tory performance of any boiler in several particu- lars. Unless sufficient steam and water capacity is provided there will not be regularity of action ; the steam pressure will suddenly rise and as sud- denly fall, and the water level will be subject to frequent and rapid changes ; and if the steam is drawn suddenly from the boiler, or the boiler crowded, wet steam will result. Water capacity is of more importance than unavoidable unequal expansion nec- essarily weakens the metal, and is a serious source of danger. Hence a boiler which makes dry steam is to be preferred to one that dries steam which has been made wet. 9.—Steadiness of Water Level. The large area of surface at the water line, and the ample passages for circulation, secure a steadiness of water level not surpassed by any boiler. 10.—Freedom of Expansion. The triangular arrangement of the parts forming a flexible struc- ture allows any member to expand without straining any other, the ex- panded connections being also am- ply elastic to meet all necessities of this kind. This is of great import- ance because the weakening effect of these strains of unequal expansion, between rigidly connected parts, is a prolific cause of explosions in ordi- nary boilers. The rapid circulation of the water, however, in this boiler, by keeping all parts at the same tem- perature, prevents to a large extent unequal expansion. Babcock & Wilcox Boiler, 120 H. P., at the H. I. Kimball House, Atlanta, Ga., Erected 1884. Showing style of Wrought Iron Front. 11.—Safety from Explosions. The freedom from unequal expansion avoids the most frequent cause of explosions, while the division of the water into small masses prevents serious destructive effects in case of accidental rupture. The comparatively small diameter of the parts secures, even with thinness of surface, great excess of strength over any pressure which it is desirable to use. So powerful is the circula- tion of the water, that no part will be uncovered to the fire until the quantity of water in the boiler steam space, owing to the small relative weight of the steam. Twenty-three cubic feet of steam, or one foot of water space, are required to supply one horse-power for one minute, the pressure meantime falling from 8o lbs. to 70 lbs. per square inch. The value of large steam room is therefore generally much overrated, but if it be too small the steam in passing off will sweep the water with it in the form of spray. Too much water space makes slow steaming and waste of fuel in start- ing. Too much steam space adds to the radiating 39