300
r to the farthermost burner. The extra cost of the larger size of pipe which the application of this rule may entail will be very slight in all ordinary house installations.
VELOCITY OF FLOW IN PIPES.--For various purposes, it is often desirable to know the mean speed at which acetylene, or any other gas, is passing through a pipe. If the diameter of the pipe is d inches, its cross-sectional area is _d^2_ x 0.7854 square inches; and since there are 1728 cubic inches in 1 cubic foot, that quantity of gas will occupy in a pipe whose diameter is d inches a length of
1728/(_d^2_ x 0.7854) linear inches or 183/_d^2_^ linear feet.
If the gas is in motion, and the pipe is delivering Q cubic feet per hour, since there are 3600 seconds of time in one hour, the mean speed of the gas becomes
183/_d^2_ x Q/3600 = Q/(19 x 7_d^2_) linear feet per second.
This value is interesting in several ways. For instance, taking a rough average of Le Chatelier's results, the highest speed at which the explosive wave proceeds in a mixture of acetylene and air is 7 metres or 22 feet per second. Now, even if a pipe is filled with an acetylene-air mixture of utmost explosibility, an explosion cannot travel backwards from B to A in that pipe, if the gas is moving from A to B at a speed of over 22 feet per second. Hence it may be said that no explosion can occur in a pipe provided
Q/(19.7_d^2_) = 22 or more;
_i.e._, Q/_d^2_=433.4
In plain language, if the number of cubic feet passing through the pipe per hour divided by the square of the diameter of the pipe is at least 433.4, no explosion can take place within that pipe, even if the gas is highly explosive and a light is applied to its exit.