This boiler consists of a cylindrical steam-receiver placed above, and communicating with, two flat water-chambers, extending down to nearly the fire-grate, and connected with a number of inclined water-tubes arranged ovr the fire-grate. The boiler, shown in Figs. 328 and 329, is suitable for triple-expansion engines of about 560 indicated horse-power. It has 1,350 square feet of heating-surface, and 40-1/3 square feet of area and fire-grate. The steam-receiver is 3 feet 5 inches diameter and 9 feet 4 inches long. The tubes are 7 feet 10 inches long, 3-1/8 inches diameter externally, 1/8 inch in thickness, and 199 in number. The ratio of the heating-surface to the area of the fire-grate is 33.5. The water contents of the of the boiler are 674 gallons, or about 3 tons. The steam-space is 81 cubic feet. The weight of the boiler with fittings, fire-grates, and casings, but without chimney, is 14 tons, without water.
A distinguishing feature of this boiler is the arrangement for securing efficient combustion of the fuel-gases. The boilers are generally arranged in pair, and a combustion-chamber common to the two boilers is formed between the two next sets of tubes. The top and bottom rows of tubes are covered with tiles. The fuel-gases, after leaving the furnace, enter the combustion-chamber, where their combustion is completed, whence they pass horizontally across the tubes, adn aare directed by a sheet-iron baffle-plate, fitted to the outer vertical row of tubes, into a smoke-box, formed under the steam-receiver, from which they flow into the uptake and funnel.
The combustion of fuel is so efficient in these boilers, that there is little variation in steam-production whatsoever be the rate of combustion.
Source: Walter S. Hutton, Steam-Boiler Construction: A Practical Handbook (London: Crosby, Lockwood, 1903).
The model of the Lagrafel d'Allest boiler now used in the French navy was introduced in 1888, and belongs to the type of water-tube boilers with flat water spaces. Like other large tube boilers, the generating tubes are slightly inclined backwards, so as to cause the generated steam to be directed towards the front. Above the generating tubes is a large cylindrical reservoir connecting the two flat water spaces, and the water level is in this chamber.
The characteristic feature of this boiler is the combustion chamber situated at the side of the grate, the boilers being all arranged in groups of two with the combustion chamber between them. Owing to its great length, equal to the length of the tubes, a small transverse width of this chamber is sufficient, and the hot gases, after passing into it, return right across the generating tubes, and escape by an opening on the opposite side of the boiler. They then pass up outside the nest of tubes, and along the top of it, embracing in their passage the lower half of the reservoir, and thence to the uptake. As the top drum is cut away in the lower half of its circumference where it joins the two water spaces, the two ends are stayed together by longitudinal stays set round in a circle.
Source: Jane's Fighting Ships, 1906-07 ed. (London: Sampson, Low & Marston, 1906), 455.
Lagrafel d'Allest boilers were adopted enthusiastically by the French navy beginning in 1888. Here is the Lagrafel-equipped Jaureguiberry on a full-power run under forced draft.
