Page:EB1911 - Volume 04.djvu/164

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BOILER
151

in the estimation of these particulars. Further, in order properly to represent working conditions, the rate of combustion of the fuel throughout the trial must be the same as that intended to be used in ordinary working, and the duration of the test must be sufficient to include proportionately as much cleaning of fires as would occur under the normal working conditions. The tests should always be made with the kind of coal intended to be generally used, and the records should include a test of the calorific value of a sample of the fuel carefully selected so as fairly to represent the bulk of the coal used during the trial. The periodic records taken are the weights of the fuel used and of the ashes, &c., produced, the temperature and quantity of the feed-water, the steam pressure maintained, and the wetness of the steam produced. This last should be ascertained from samples taken from the steam pipe at a position where the full pressure is maintained. In order to reduce to a common standard observations taken under different conditions of feed temperatures and steam pressures, the results are calculated to an equivalent evaporation at the atmospheric pressure from a feed temperature of 212° F.  (J. T. Mi.) 

Trials of Various Types of Marine Boilers

Description of Boiler. Grate 
Area
sq. ft.
Heating
Surface
sq. ft.
Duration
of Trial
Hours.
Coal
burned
Per sq. ft.
of Grate
per Hour.
Air
Pressure
in Stoke-
hold—
Inches of
Water.
Chimney
Draught—
Inches of
Water
Water Evaporated
per ℔ of Coal.
Water
Evapor-
ated per
sq. ft. of
Heating
Surface.
Thermal
Units per
℔ of
coal.
 Efficiency 
of
Boiler
%.
Actual. From and
at 212° F.
℔. ℔. ℔.
Ordinary cylindrical single-
 ended; 3 furnaces; 155 ℔
 working pressure; closed
 stokehold system.*
 81 2308 25 14.2 Nil 0.36  8.56 10.26 4.26 14,267 69.7
 ” 24 13.9 0.50  8.84 10.33 4.32 14,697 68.0
 ”  9 30.3 0.81 0.39  7.93  9.27 8.46 14,686 61.4
 ”  81/2 29.1 0.65 0.32  8.84 10.34 9.05 14,612 68.4
Ordinary cylindrical single-
 ended; 3 furnaces; 210 ℔
 working pressure; closed
 ashpit, Howden system.**
63.2 2876 in boiler,
766 in air
heaters
13 20.6 In Ash-
pit
1.53
0.58 11.30 12.33 5.14 14,475 82.3
Niclausse water-tube; 160
 ℔ working pressure.
 46 1322  8 12.8 Nil 0.20  8.41 10.15 3.75 14,680 66.9
 ”  8 21.9 0.20  8.01  9.40 6.11 14,760 62.1
 ” 37 20.2 0.29  7.62  9.00 5.44 14,600 60.5
Niclausse water-tube;
 250 ℔ working pressure.
 34 990  9 14.0 0.10 0.23  8.77 10.50 4.17 14,640 69.8
 ”  9 22.0 0.27 0.23  7.68  9.06 5.74 14,640 60.4
 ” 90 15.4 Nil Not asce-
rtained
 7.61  9.08 4.00 14,630 59.9
Babcock water-tube; 33/16
 in. tubes; 260 ℔ working
 pressure.
 36 1010  9 13.0 0.26  9.31 11.02 4.30 14,590 73.2
 ”  9 20.0 0.18 0.20  8.58 10.11 6.13 14,590 67.0
 ” 90 14.5 Nil Not asce-
rtained
 8.09  9.53 4.18 · · 63.1
Babcock water-tube; 113/16
 in. tubes; 270 ℔ working
 pressure.***
 62 2167 28 18.4 0.45  8.94 10.61 4.61 14,520 70.7
 ” 24 19.2 0.47  8.93 10.59 4.82 14,390 71.1
 ” 12 20.5 0.42  9.42 11.04 5.41 14,080 75.8
 ”  7 28.9 0.50 Not asce-
rtained
 8.54  9.88 6.91 14,390 66.3
 ” 30 19.9 Nil 0.38 10.11 12.00 6.01 14,530 79.9
 ” 29 27.1 0.66 0.23  9.96 11.67 8.05 14,630 77.1
Belleville water-tube with
 economizers; 320 ℔
 working pressure.
 44 910 in boiler; 241/2 15.8 Nil 0.36  9.65 11.46 4.94 14,697 77.2
 ” 447 in econo- 24 17.4 0.39  9.33 11.00 5.30 14,805 71.8
 ” mizer; 11 19.8 0.43  9.39 11.03 6.38 14,578 73.3
 ” 1357 total.  8 27.2 0.39  8.28  9.79 7.78 14,611 65.0
Yarrow water tube; 13/4 in.
 tubes; 250 ℔ working
 pressure.
 56 2896 26 16.9 Nil 0.31  9.57 11.45 3.12 14,750 75.0
 ” 26 18.2 0.31  9.37 11.33 3.30 14,500 75.7
 ” 25 21.3 0.31  8.83 10.45 3.63 13,500 75.2
 ” 30 35.4 0.53 0.26  8.82 10.59 6.04 14,430 70.9
 ”  8 41.9 0.86 0.31  8.24  9.94 6.69 14,500 66.3
 ”  8 33.7 0.31 0.30  8.39  9.93 5.47 14,680 65.4
 ”  8 39.8 0.82 0.24  8.85 10.43 6.81 14,530 69.5
Dürr water-tube; 250 ℔
 working pressure.
 71 2671 in boiler,
140 in super-
heater;
2811 total.
26 16.1 Nil 0.39  7.95  9.50 3.24 14,500 63.8
 ” 26 17.7 0.30  7.06  9.28 3.43 14,620 61.7
 ” 25 21.1 0.31  7.62  9.08 4.05 14,650 60.3
 ”  7 33.8 0.70 0.36  7.72  9.29 6.59 14,570 62.7
 ”  8 26.7 0.33 0.35  7.86  9.26 5.30 14,320 63.1
 ”  8 34.6 1.11 0.20  8.02  9.53 7.02 14,230 64.8
 ” 22 34.8 0.73 0.16  6.84  8.06 6.02 14,430 54.0
 ” 24 29.9 0.35 0.12  7.62  9.00 5.75 14,240 61.2
 ” 20 19.9 Nil 0.21  7.30  8.33 3.66 14,240 58.6
*  In the first three trials no retarders were used in the tubes. In the last trial retarders were used.
**  In this trial retarders were used in the tubes.
*** The first four trials were made with horizontal baffles above the tubes; the last two trials with the baffling described in the text.

Boiler Making

The practice of the boiler, bridge and girder shops may here be conveniently treated together, because similar materials and methods are employed in each, notwithstanding that many points of divergence in practice generally relegate them to separate departments. The materials used are chiefly iron and steel. The methods mostly adopted are those involved in the working of plates and rolled sections, which vastly predominate over the bars and rods used chiefly in the smithy. But there are numerous differences in methods of construction. Flanging occupies a large place in boilermaking, for end-plates, tube-plates, furnace flues, &c., but is scarcely represented in bridge and girder work. Plates are bent to cylindrical shapes in boilermaking, for shells and furnaces, but not in girder work. Welding is much more common in the first than in the second, furnace flues being always welded and stand pipes frequently. In boiler work holes are generally drilled through the seams of adjacent plates. In bridge work each plate or bar is usually drilled or punched apart from its fellows. Boilers, again, being subject to high temperatures and pressures, must be constructed with provisions to ensure some elasticity and freedom of movement under varying temperatures to prevent fractures or grooving, and must be made of materials that combine high ductility with strength when heated to furnace temperatures. Flanging of certain parts, judicious staying, limitation of the length of the tubes,