Pneu-mat′ic drill.
A drilling-machine operated by compressed air admitted alternately above and below a piston connected with gear-wheels which rotate the drill.
The air-reservoir and force-pump may be placed at any required distance from the cylinder, and connected therewith by a flexible pipe.
Fig. 3847 is
Burleigh's pneumatic drill,
a is a pipe by which air is brought from the compressed air-chamber;
b c, the cylinder, provided with proper valves for admitting the air alternately above and below the piston and for exhaust.
The drill
d is attached directly to the piston-rod, and is driven down by the admission of air above the piston, and retracted when the air is admitted below, giving from 150 to 250 blows per minute.
The cylinder, with the piston and drill, is advanced by the screw
e as the drill penetrates the rock, the drill being rotated at the same time.
Five sizes of drill, forming holes from 1 1/4 to 5 1/2 inches diameter, may be used, the engine being of about three horsepower with a pressure of 50 pounds to the square inch.
A small amount of power is lost by the transference of the air from the surface of the ground when the apparatus is employed in subterranean operations in mining or tunneling, but this is more than compensated by the cooling and ventilation effected by the exhaust.
The cylinder, with its working apparatus, is rotatable vertically on trunnions for varying the direction of the blows given by the drill
By the
pneumatic drill, the
Mt. Cenis Tunnel, seven miles in length, was bored through the
Alps.
The Hoosac Tunnel in
Massachusetts, five miles in length, was cut by the same means.
Compressed air is also used in the
St. Gothard Tunnel in
Switzerland, lately commenced, which is to be 13 miles in length; and also in the operations at Hell-Gate,
East River, N. Y. Sec submarine excavation; tunnel.
