Newcomen and the other early developers of steam engines and boilers were not simply inspired mechanics making discoveries more or less by chance. They had a good knowledge of their subject and each advance in pressure, temperature and combustion was based on a conscious search for greater efficiency and larger power output from smaller machines. This led to a steady improvement in engines. Steam boilers also improved, but reached a plateau in the mid-nineteenth century due to the limitations of the commonly used fire tube boiler in pressure, temperature, unit output, and safety.
Many men worked on the solution of this problem -- which called for the development of a safe water-tube boiler. Stephen Wilcox applied his knowledge of water circulation theory to find the proper answer, resulting in the Wilcox Patent of 1856. An improved model was patented in 1867, at which time George Babcock and Stephen Wilcox formed their partnership.
The water-tube boiler was an open-ended invention -- its development has been continuous to this day -- and shows no signs of stopping. The advent of central stations for generating electricity in 1881 opened a vast new market for B&W boilers. The original Babcock & Wilcox boiler had been continuously improved since 1867 and it was about that time the boiler represented by the model was introduced. Thousands of these boilers have been sold, and even today a few are being sold abroad for special purposes. Many are still in use, especially abroad. The design, with modifications, was B&W's standard for many years and was only superseded by other designs when the demand for high pressures and temperatures and greatly increased individual boiler capacity made changes beneficial.
The 20th edition of STEAM, ITS GENERATION AND USE, published by Babcock & Wilcox in 1889, describes the boiler's construction, erection and operation as follows:
This boiler is composed of lap-welded wrought iron tubes, placed in an inclined position and connected with each other, and with a horizontal steam and water drum, by vertical passages at each end, while a mud-drum connects the tubes at the rear and lowest point in the boiler. The end connections are in one piece for each vertical row of tubes, and are of such form that the tubes are "staggered" (or so placed that each horizontal row comes over the spaces in the previous row). The holes are accurately sized, made tapering, and the tubes fixed therein by an expander. The sections thus formed are connected with the drum, and with the mud-drum also by short tubes expanded into bored holes, doing away with all bolts, and leaving a clear passage way between the several parts. The openings for cleaning opposite the end of each tube are closed by hand-bole plates, the joints of which are made in the most thorough manner, by milling the surface to accurate metallic contact, and are held in place by wrought iron forged clamps and bolts. They are tested and made tight under a hydrostatic pressure of 300 pounds per square inch, iron to iron, and without rubber-packing, or other perishable substances.
The steam and water drums are made of flanged iron or steel, of extra thickness, and double riveted. They can be made for any desired working pressure, but are always tested at 150 pounds per square inch unless otherwise ordered. The mud-drums are of cast iron, as the best material to withstand corrosion, and are provided with ample means for cleaning.
In erecting this boiler, it is suspended entirely indepedent of the brick-work, from wrought iron girders resting on iron columns. This avoids any straining of the boiler from unequal expansion between it and its enclosing wall, and permits the brick-work to be repaired or removed, if necessary, without in any way disturbing the boiler. All the fixtures are extra heavy and of neat designs.
The fire is made under the front and higher end of the tubes, and the products of the combustion pass up between the tubes into a combustion chamber under the steam and water-drum; thence they pass down between the tubes, then once more up through the spaces between the tube, and off to the chimney. The water inside the tubes, as it is heated, tends to rise towards the higher end, and as it is converted into steam -- the mingled column of steam and water being of less specific gravity than the solid water at the back end of the boiler -- rises through the vertical passages into the drum above the tubes where the steam separates from the water and the latter flows back to the rear and down again through the tubes in a continuous circulation. As the passages are all large and free, this circulation is very rapid, sweeping away the steam as fast as formed, and supplying its place with water; absorbing the heat of the fire to the best advantage; causing a thorough commingling of the water throughout the boiler and a consequent equal temperature, and preventing, to a great degree, the formation of deposits or incrustations upon the heating surfaces, sweeping them away and depositing them in the mud drum whence they are blown out.
The steam is taken out at the top of the steam-drum near the back end of the boiler after it has thoroughly separated from the water.
Advantages claimed "over those of the ordinary construction" were:
1. Thin heating surface in furnace
2. Joints removed from the fire
3. Large draught area
4. Complete combustion
5. Thorough absorption of the heat
6. Efficient circulation of water
7. Quick steaming
8. Dryness of steam
9. Steadiness of water level
10. Freedom for expansion
11. Safety from explosions
12. Operations at capacity
13. Accessibility for cleaning
14. Least loss of effect from flue dust
16. Ease of transporation
17. Freedom from, and ease of repairs
18. Advantages demonstrated by practical experience
A copy of B&W's publication HIGH PRESSURE, published in 1895, is attached. It provides additional information not only about the construction details, but also illustrations of B&W's manufacturing facilities and competitive boilers of the time.