1873 - Old Forge Coal Mines

62 ANNUAL REPORT OF THE
The work is done before the steam is cut off=2 feetX20 lbs., pressure=
40 lbs. plus 36.61 lbs=76.61 lbs., minus work done against the piston by
the vapor in the condenser=4 lbs.X5 feet—20 lbs.
These vaWes give 36.61 plus 40 minus 20=56.61.
When total work on 1 inch of piston=56.61 pounds.
Example 3.—Two oscillating marine engines, (condensers,) whose cylinders
are 42 inches in diameter, and steam admitted by the elastic force of
20 lbs. per square inch ; the length of stroke being 3 feet and 1 inches,
making 30 strokes per minute, and working with piston rods 5 inches in
diameter. It is desired to know what these valves will work up to in effective
horse-power.
General Rule for Finding Power op
Engines.
Square the diameter of the piston in inches and parts, deduct half the
circular area of the piston rod, multiply .7854, multiply length of stroke in
feet and decimal parts, multiply the numoer of strokes per minute, multiply
the number of pounds pressure per square inch of safet}^ valve, minus
one-fifth (I) of the whole for modulus or friction, and divide by 33000, or
equal horse-power.
In the above example,
42X42—12.5, half are of piston rodX. 7854X3.83X30X20
_i=76.635 horse-power
33000.
of one engine ; hence 76.635+76.635=153.270
horse-power, the same valves working 23^ strokes per minute, gives 120
horse-power.
Steam Ships.
How to ascertain the speed of a steam ship with revolving paddles.
Rale.—A steamer of 17 feet 6-inch paddle-wheel, the rims of the wheels
being 4 inches broad, for which deduct twice 4 inches and 1
inch clearance
for working, brings the wheel to 16 feet 9 inches diameter, making 30 revolutions
per minute. How many miles per hour ?
Here— 16 feet 9 inchesX3.1416=52.6218, or 52 feet 7£ inches=l revolution.
Then 52.6218X30 revolutions X 60 minutes-=-3 feet, or 1 yard-=-
1,760 yards for miles=17.93 miles, or 18 miles nearly per hour ; and 60
minutes-=-l 7.93=3.34, or 3 minutes and 20 seconds in completing 1 mile.
This rule can be relied upon as being correct.
Horse Power op Steamers, Paddle-Wheels.
Suppose the four engines that propel the paddles of the Great Eastern
to have steam of the elastic force of 20 pounds to the square inch admitted
into the cylinders; the pistons moving through 140 feet of space in one
minute, thus describing 10 revolutions per minute, or equal 14 feet each
per minute ;
the diameter of pistons being 74 inches each, the piston rods
being 9 inches each in diameter. It is desired to know the horse-power
that these values will give.
Here: 74X74—\ area of 9 inches for piston rodsX7,854X10X10X20
_l-5=9562G53,40800-r-33000=289.77=horse-power of these engines. This
rule holds good for all such measurements.
Pumping Engine Work Considered.
Suppose an engine drawing water from a mine 100 fathoms deep, through
the aid of three sets of pumps ; the bottom set lifts the water 50 fathoms,