550
MOLESWORTH’8 POCKET-BOOK
Pneumatic Transmission (‘Min. Inst. Civ. Eng.,’ vol. xlill.)
Leaden tubes are generally used.
The 3 diameters used are 3, if, 1;.
The relative traffic power of the tubes was as follows:—
Time required for Traffic. Power required.
3"..............100..................................100
2\............ .. 116................... 49
li.................141.................. 18
The lowest possible diameter for the traffic should be
adopted.
Tubes are made in lengths of 29 feet, smoothed Inside by a
Fteel mandrel, lubricated with soft soap, and drawn through to
make the bore fair and uniform.
Minimum radius of curves of the pipe, 12 feet.
The carrier is a cylindrical box of gutta-percha covered
with felt; the felt projecting slightly in the rear of the carrier.
The open end of the carrier is closed by an elastic band, to
prevent the messages from escaping.
Tubes should be worked on the block system if worked by
pressure; but, if worked by a vacuum, where there is no
intermediate station, carriers may follow at short intervals.
Signalling is done by electric telegraph.
Obstructions are removed by forcing water into the pipe
when they cannot be removed by air.
The distance of a fault is ascertained by firing a pistol into
the tube, and calculating the distance from the time the con-
cussion of air travels to, and is reflected back by, the obstacle ;
the rate for calculation being 1030 feet per second.
Engines compound; high-pressure cylinder 17 in. diam.
49} stroke; low-pressure cylinder 25i in diam. 66 stroke.
Boiler, pressure 70 lbs. per square inch.
Each engine indicated 73i horse-power at 25 revolutions
per minute.
The compressing pump indicated 3' J HP.
And vacuum „ „ 26| ,,
Total .. .. 62| „
Efficiency = ‘312. Compression of air = 10 lbs. above
atmosphere; vacuum = 8'8 lbs. below atmosphere.