The Locomotive - Lighthouse Survival Blog

52 THE LOCOMOTIVE. [April,
above), and multiply the product by the "modulus of elasticity " of the material of the
pipe (which, in the case of wrought iron, is about 29,000,000) ; then divide by the dis-
tance from the boiler to the blow-cock (expressed in feet), and take the square root of
the quotient. The result so obtained will be the greatest total pull (in pounds) on the
material of the pipe that can be caused by the sudden stoppage of the flow of water
within it.
The area of metal in the cross-section of a 3-inch pipe is about 2.23 square inches,
and the " kinetic energy" of the water (or the energy due to its motion) we have already
found to be 2,304 foot-pounds. Hence the calculation is as follows:
2.23x2x2,304x29,000,000=298,000,000,000.
The distance from the boiler to the blow-cock being 5.5 feet,
298,000,000,000^-5.5=54,200,000,000.
we then have
The square root of this is 233,000; and therefore the maximum stress that could be
thrown on such a blow-off pipe, by the instantaneous stoppage of the solid column of
water moving through it with a velocity due to 60 pounds of steam, is 233,000 pounds.
There being 2.23 square inches of metal in the cross-section of a 3-inch pipe, it follows
that the greatest possible stress that could come upon the material of the pipe, from the
sudden stoppage of the stream of water within it, is 233,000-^2.23 = 104,000 pounds
(in round numbers) per square inch; which is greater than the tensile strength of steel.
We do not pretend that such an enormous stress as this could be actually realized
in a blow-off pipe, because in performing the calculation we have made various assump-
tions that cannot be rigorously fulfilled in experience. The most important of these is,
that the cock is closed instantly. Xow a fireman might be able to close the cock in a
fraction of a second, but he certainly could not do it literally "in no time." The
quicker he works, the nearer he will approach to the figures given above; but he can
never come very close to them, no matter how spry he may be. Another important
assumption that we made, is that the blow-pipe is filled with solid water, even when the
cock is open. This cannot be the case, for the pressure in the pipe, while the current is
passing, is less than that in the boiler, and hence a certain proportion of the contents of
the pipe must be steam.
It is not worth while to discuss all these minor matters in detail, however. The
main object of the calculation given above is to show that it is theoretically possible,
under certain ideal conditions, to throw a stress on the blow-pipe, merely by closing the
cock, which w T ill be great enough to pull a sound steel pipe in two. "When we come
to the practical question of how great a stress could be realized in practice, all we can
sav is, that after making all reasonable allowances and deductions, there is still abun-
dant reason for believing that the stresses actually produced by the too sudden closing
of a blow-cock may be quite severe enough to break a fitting, or strip the threads from
a pipe, especially when (as is often the case) the pipe-fitting is none too perfect.
The only safe way to close a blow-cock, is to turn it off slowly, so that the opera-
tion takes several seconds, at least.
Boiler Explosions.
January, 1901.
(1.) — On January 1st a boiler exploded in Hitchcock's mill, between Johnson &
Cortland, near Warren, Ohio. The owners, Edward and Lucius Hitchcock, were
instantly killed, and their bodies were blown to pieces. Charles Shaw, Bernard Buell,
and Charles Schreit were injured. Shaw was injured internally, and may die. The
mill was completely demolished.