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Boiler Diameter.—Having decided how many square feet of tube heating surface the boiler should contain, what diameter and length the tubes should be, and what widths of water space are to be left between the tubes, the above table will enable one to estimate how many square inches of tube plate area will be taken up by the tubes. These areas are represented by A and B (fig. 434), and the various letters indicate the other water and steam spaces, viz.: a is the distance between
two furnace diameters. b is the distance between
the furnace and the
shell. c is the distance from the
TC e is the distance from the
centre furnaces to the
lower row of tubes. f is the distance from the shell to the wing tubes.
1 h is the same dimension
I measured in the steam
--Dspace. g is the distance between
FIG. 434 the nests of tubes. All these dimensions are to be taken, not from centre to centre, nor from the circumferences, but from the squares surrounding the tubes, as shown in fig. 435.
Let (T) represent the sum of the end space required for the tubes. In fig. 434 this would be 2A + B. Let ū be the boiler diameter, then, I (T) = 0.45(D-d-K).
The value of K is found by multiplying the various water and steam spaces by the numbers contained in the following table, and then adding them together : Number of Furnaces in Boiler ,
The above formula will be found to agree fairly well with the general practice as long as his equal to one-third of the boiler diameter (3D). Where this relation does not exist, subtract from D, Žin., 1 in., and 1} in., for two, three-, and four-furnaced boilers respectively, for every additional inch of steam space, so that if written out in extenso the above formula would beFor two furnaces : 3
D--d--20(a +36+28+, (e) + $ (9)]
+ 3(e) + 2 (9)])"
For three furnaces :
* (T)=0-45(D-h-d=7a+6b+.2c+i4f+-25%3(e) +3(9))".
For four furnaces :
* (T)=0-45()! —-—d="45(a+b)+35 [2C+(e)+Š(9)+355) ?
The sign I ( ) means that the letter in the bracket is the sum of the several dimensions.
These formulæ can be simplified by adopting the following average values : a and b vary from 3 ins. to 8 ins., and are usually 5 ins.
In two-furnaced boilers c varies from 3 ins. to 11 ins., but it is generally made 7 ins. In other boilers it varies from 8 to 12 ins., the mean being 10 ins.
e is sometimes as much as 15 ins. Generally both c and e are made 10 ins.
f and g both vary from 8 ins. to 12 ins. The usual practice is to make both about 10 ins. ; this would give 10. ins. of clear water space at the wings, and 11 ins. at the centres.
The mean value of h is } D.
Substituting these average values, the formulæ are reduced to the following: For two furnaces and two combustion chambers
(T) = 0.45 (D-d-12})?
(T) = 0:45 (D-d-22).
For four furnaces and two combustion chambers-
(T) = 0·45 (D-d—242)?. For four furnaces and three combustion chambers
(T)= 0·45 (D-d—281). For the purpose of ascertaining the diameter it will be more convenient to alter these formulæ as follows:
The Length of the Boiler is fixed by the length of the tubes or furnace, by the depth of the combustion chambers, and by the water space at their backs.
The latter should not be made less than 5 ins., but cases are met with where they are reduced to 3 ins. They should be made wider at the top than at the bottom, the usual angle being } in. per foot of depth.
The Combustion Chambers, measured horizontally, should be made as deep as possible : 28 ins, and 36 ins. seem to be the smallest limits for single- or double-ended boilers respectively. Generally this depth is about 12 ins. greater than half the furnace diameter for single-ended boilers, while for double-ended ones with through combustion chambers it is made about 24 ins. deeper than half the furnace diameter.
The following are the relations usually existing between various boiler dimensions :
Boilers with Two Furnaces. The ratio of boiler diameter to furnace diameter is generally as 10 to 3, but sometimes 10 % more or less. Custom is equally divided between leading the two furnaces into two combustion chambers or into one. In the latter case the central water space between the tubes is sometimes dispensed with, but generally a few rows of tubes are left out along this line. The diameters of these boilers range from 8 ft. to 14 ft., and the lengths from 8 ft. to 10 ft. for natural draught, and up to 12 ft. for forced draught. The shortest double-ended boilers are 12 ft. long, and the longest 18 ft.
Boilers with Three Furnaces.—The ratio of boiler diameter to furnace diameter is generally as 4 to 1, but sometimes 7 % more or less. Generally three combustion chambers are fitted, but sometimes only one, and in that case the tubes are mostly divided into two groups with a water space in the centre. In rare cases there are no water spaces except at the sides. The diameters of these boilers range from 11 to 16 ft., and the lengths from 9 to 11 ft. for natural, and 12 ft. for forced draught. Double-ended boilers are sometimes made 20 ft. long.
Boilers with Four Furnaces.-The ratio of boiler diameter to furnace diameter is generally 5 to 1, but sometimes 5 % more or less. The combustion chambers are usually so arranged that the two central furnaces are led into one, and the two wing ones into separate chambers, so that there are one large and two small ones. Sometimes there are only two combustion chambers, and very rarely there are four, or only a single one. The diameters range from 13 to 17 ft., and the lengths are the same as for three-furnaced boilers. Double-ended ones are rarely built.
Boiler Performances. The following are a few rough rules for estimating the heating surface and power of a boiler under natural draught :
D = boiler diameter in feet.
P= working pressure in pounds per square inch.
Q=boiler weight in tons (no funnel, &c.).
C= coefficients. IHP= indicated horse-power = from d to HS and up to 1 HS with forced .draughts. With water tube boilers these coefficients have to be reduced about 25 %.
HS = C, D2.L
Q=C2 (D? . L + HS) (P + 60). 1:0, = 27,000 for single-ended boilers to Lloyd's Rules. 1:02 = 25,700 for single-ended boilers to Board of Trade Rules. 1:C2 = 30,000 for double-ended boilers to Lloyd's Rules.
28,600 for double-ended boilers to Board of Trade Rules. W= 0.01 D2L.
In 1898 on the Clyde and before the recent rise in prices, the cost of single.ended boilers working at 150 pounds and designed to Lloyd's Rules, not including funnel, &c., was
Cost in £= 0:35 D. L + 2 (D2L) 8/9. The first term represents the cost of material and such charges as are nearly proportional to weight, and therefore to pressure ; the second term represents such charges-as riveting, tapping, screwing, caulking -as are nearly proportional to the boiler surfaces.
All the above coefficients vary in different works, as they depend on local practices and appliances.
The following are a few published details of boiler weights. Bertin & Robertson, p. 355, Weights of Water-tube Boilers’; also Norman,'' Enging.,' vol. lviii. p. 701 ; Kensington,'' Enging.,' vol. lviii. p. 199; U.S. - Minneapolis,'' Enging.,' vol. Ix. p. 600.
Two lists of boiler performances have been published by F. Marshall, M. E.,' 1881, p. 449, and 1891, p. 337.
The following is a list of published drawings of marine boilers :
F. Colyer, 1886. Three-furnaced oval boiler, by Maudslay, 12 ft. 4 ins. diam., 14 ft. 1 in. diam., 9 ft. 11 ins. long; three-furnaced cylindrical boiler, 17 ft. 4 ins. diam., 9 ft. 1 in. long.
Schwarz Flemming, 1873. Forty-nine sketches of boilers.
J. T. Winton, 1883. Various types of boilers.
N. P. Burgh, 1873, contains drawings of about 20 boilers and sketches of 90 types of patented boilers from 1852–71.
N. Foley, 1891. Plates 6, 7, 8, give full detailed drawings of the three following boilers :
Single-ended, 2 furnaces, 39 ins. internal diam., 1,099 sq. ft. heating surface. Outside dimensions, 12 ft. x 9 ft. 8 ins. Weight, 25 tons. Steam pressure, 150 lbs.
Single-ended, 3 furnaces, 35} ins. internal diam., 1,334 sq. ft. heating surface. Outside dimensions, 12 ft. 6 ins. x 9 ft. 8 ins. Weight, 27 tons. Steam pressure, 150 lbs.
Double-ended, 4 furnaces, 34 ins. internal diam., 1,843 sq. ft. heating surface. Outside dimensions, 10 ft. 6 ins. x 16 ft. 6 ins. Weight, 34 tons. Steam pressure, 160 lbs. (See also p. 316.)
Other types of boilers will be found in the following lists ::
Navy Type. - Surprise' and 'Alacrity,'Palmers', 'Enging.,' vol. xl. pp. 447, 450; Melbourne,' Simmons & Co., ‘Engr.,' vol. Ix. p. 392 ; Yorktown,'' Enging.,' vol. li. p. 493; ‘Bergen,' Enging.,' vol. xlix. p. 191 ; · Mouche,' Belliss & Co., * Enging.,' vol. xxxix. p. 81; 'Enging.,' vol. lv. p. 694.
Locomotive Type.-Schichau, ‘Enging.,' vol. xxxiv. p. 579; Yarrow, 'Enging., vol. xlii. p. 179; “Sunderland, Doxford, ‘Enging., vol. xlix. p. 30 (for burning petroleum); Hick, Hargreaves, Enging.,' vol. xlix. p. 528; · Barham' and · Bellona,' Hawthorn, Leslie & Co., * Enging.,' vol. 1. p. 705; ‘Phlegeton,' Soc. Ann. Claparede, ‘Engr.,' vol. Ix. p. 277; Sectional locomotive boiler for transport, Sandycroft Foundry, Enging.,' vol. xxxviii. p. 261; N. Foley, 1891, pl. x. and xi.; 'Enging.,' vol. lv. p. 695; H.M.S. Hazard, Enging.,' vol. lviii.
Water Tube Boilers.-J. F. Spencer, M. E.,' 1859, p. 264 ; Z. Colburn, ibid., 1864, p. 61; Laybourne, ibid., 1871, p. 263; D. Joy,
I. and S. I.,'1874, p. 220 ; Perkins boiler, Maw, cii.; Adams and Co., Enging.,' vol. xxxiv. p. 251; J. F. Flanery, ‘C. E.,' 1878, vol. liv. p. 123; J. T. Thornycroft, Enging.,' vol. xxxv. p. 463, vol. xliv. p. 105, vol. xlvii. p. 402; N. A.,' 1889, vol. xxx. p. 271 ; C. E.,' 1890, vol. xcix. p. 41 ; Ward's Patent, 'Enging., vol. xlvii. p. 322 ; Yarrow, ‘Enging.,' vol. li. p. 79. All recent vessels of the French Navy are having tubular boilers fitted (Belleville, Lagrafel-D'Allest), J. T. Milton, 'N. A.,' 1893, vol. xxxv. Danish cruiser Geiser' (Thornycroft),
Enging.,' vol. liv. p. 789; “Daring’ (Thornycroft), 'Enging.,' vol. lvi. p. 667 ; ‘Algerie’ (Babcox and Wilcocks), ‘Enging., vol. lviii. p. 433; Stirling Boiler, ‘Enging.,' vol. lix. p. 825 ; Stirling type,
Enging., vol. lix. p. 825; H.M.S. Terrible' (Belleville details), · Enging.,' vol. lix. p. 822; Du Temple, 'Enging., vol. lx. p. 57; Normand, ‘Enging., vol. Ix. p. 75;, H.M.S. ' Surly,' 'Enging., vol. lx.
p. 630 ; Niclausse, ‘ Enging.,' vol. lx. p. 91 ; Thornycroft, Enging.,' vol. lx. p. 269; Ligaudy, Enging.,' vol. lx. p. 541; Serpollet, 'Enging., vol. lx. p. 501 ; Haythorn, “Enging., vol. lx. p. 680; Russian Kherson (Belleville), Enging.,' vol. Ixii. p. 799 ; H.MS. *Spanker' (Du Temple),‘ Enging.,' vol. Ixiii. p. 777 ; H.M.S. ' Pelorus' (Normand), Enging., vol. Ixiii. p. 385; Laos '(Belleville), · Enging.,'