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Proportions of LoCOMOTIVE TYPE, OR Portable, Boilers.
Cylinders of Portable Engines.
PLATES FOR 70 Lbs. PRESSURE.
Ft. Grate Area in Sq.
| Horse-power. So-called Nominal
Stroke. | Smoke-box.
cluding the Length, in
120 150 170 190 210
in Sq. Ft. Heating Surface
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LANCASHIRE AND CORNISH BOILERS.
The Lancashire boiler has attained, perhaps, the highest position as a steam raiser for land purposes, and has done so by reason of its undoubted merits of simplicity and accessibility. Its construction is so well known that it is unnecessary to devote space to a description longer than to say that it consists of a shell, or tube, closed at both ends, and pierced from end to end by two fire-flues or tubes, as against one in the Cornish boiler. In these fire-tubes the furnaces are situated, and the flame is led by brick fues along the sides and under the bottom of the boiler to the chimney. The boiler is usually made from 6 feet to 7 feet diameter, and any excess of power required over that dimension it is usual to supply by additional boilers, where, placed in batteries of two or more, they can be readily stoked and managed by a very little increase in labour. For all permanent plants, where the power exceeds 100 horse-power, and economy both in fuel and in labour are looked for, the choice must lay between the Lancashire and a tubulous boiler.
In the Lancashire form is included the excellent improvements effected by the well-known Manchester firm, whose type of furnace, and their cross and tapered tubes, have given a title to the boiler they make.
The calculation of the internal tubes of Lancashire and Cornish boilers is a matter requiring care, and is the subject of a number of rules. It is the part of the boiler most liable to cause accident from its being subject to compressive strain, which, when the plates become overheated when short of water, may buckle the plate and cause collapse of the tube.
The safe working pressure for iron tubes as well as for steel may be found by the following rule :
t= thickness of the plate in inches.
ening rings or flanges.
And the proper thickness of plate is to be found thus, pressure being known or assumed :
The effect of cross tubes in the strength of flues is not greatly to increase their strength, though in case of a collapse of the tube, they may mitigate its serious effects. They should not, therefore, be taken into account in calculating the strength of a flue. From an economic point of view they do good work, greatly increasing the circulation from the dead water below the tube to the heated surfaces above, and are strongly to be advised. Their cost is always an addition to the boiler, averaging £3, or $15, each, riveted in place.
Lancashire boilers are now made up to 8 feet diameter, for working pressures of 100, 120, 140, and even 160 lbs. per square inch. For certain positions they may be beneficial, but should not be decided upon until the merits of “ water-tube” or tubulous boilers have been studied.
For high-class electric installations, where pressures have
a tendency to be fixed at the higher figures mentioned, the latter type has of late secured the preference.
The following are good sizes of Lancashire boilers, well proportioned as to diameter and length, and may be accepted as an average for a pressure of 80 lbs. per square inch :
The only difference in the Cornish boiler is that it has one flue instead of two, as in the Lancashire form.
Cornish boilers are made from 3 feet diameter to 6 feet, after which dimension two flues become advisable. Their proportions are of infinite variety between these sizes and lengths from 7 feet to 30.
The following are sizes selected as average to afford comparison of costs :
CORNISH BOILERS FOR 70 LBS. WORKING PRESSURE.
| Cost, Complete with Fittings.
Inches. 7 6
19 10 0
298 = $490
£122 = $610
£163 = $815
Setting Boilers.-In Lancashire and Cornish boilers the cost of the “setting ” forms a large proportion of their expense.
They should be sustained in position on special shaped fire-bricks, which are supplied by all the leading firms dealing in such material.
The side flues are nearly arched over by special firebricks of a half-arch shape.
Width, 1178" each.
For a boiler 28 feet long provide of each of above, 60
In addition, provide for setting a 28-feet boiler the following materials :
Quick lime...................... 29 bushels.
.... 144 “
..... 36 " Ordinary bricks ..................four thousand. Red bricks for surface work. ....... nine thousand.