STATIONARV ENGINES.
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to find the diameter of a cylinder of a Cornish engine sufficient to
raise 7,000,000 gallons of water 120 feet high in 24 hours. Multi-
ply the number of gallons by 10 (the weight in lbs. of a gallon of
fresh water), and then by the height; divide the product by the
number of hours reduced to minutes, and the quotient gives the
number of lbs. raised 1 foot high per minute, which divided by 1000
gives the area of the cylinder. Thus:
7000000 x 10 x 120 „ „„
--—-= 5833333 1000 = 5833.
I 44°
which equals 86 inches diameter nearly; to which must be addedan allowance for the friction of the engine. The divisor used mayvary, owing to the pressure and velocity, and on this account threeeminent firms have used in their practice 926, 1113, and 1140respectively; but the average of a number of Cornish enginesis 771.
Steam valves for Cornish engine :—
The steam valves. = -gVth to nVth of the cylinder area.
The equilibrium valves. = ^th to -^th ,, „
The exhaust valves. = to ^th ,, ,,
To find the duty of an engine. —Supposing an engine required3 lbs. of coal per indicated horse-power per hour, it is required tofind the duty performed by 112 lbs., or a cwt. of coal. The horse-power being 33,000 lbs. raised 1 foot high in a minute, or 1,980,000lbs. raised I foot high in an hour—then by the rule of three we have
lbs. lbs. lbs. lbs.
3 : 1980000 : : 112 = 73920000
raised I foot high by a cwt. of coal per hour. Formerly the dutywas estimated by the bushel of coal, weighing 94 lbs., but it isconsidered most convenient to adopt the 112 lbs. measure. Theaverage duty of Cornish engines may be taken at 60,000,000 lbs.raised 1 foot high in one hour by a bushel of coal weighing 94 lbs.,or 71,489,361 lbs. with a cwt. or 112 lbs.
The power required to overcome the friction of water through pipes.—When water is required to be pumped through a long line ofpiping an allowance is generally made for its friction in transit. Thequantity of water in cubic feet per minute, and the diameter andlength of the line of piping being given, multiply the square of thequantity in cubic feet by the length of the piping in feet, and dividethe product by the constant 22 for pumping engine, multiplied by
the fifth power of the diameter of the piping. Thus, supposing
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