Page:Walker (1888) The Severn Tunnel.djvu/158

Rh underground through this heading, we succeeded in putting in the bottom and 20 or 30 feet of the shafts without having any water to contend with.

In a heading being driven at any distance from the shaft, though there may be but five or six men in the heading, the heat becomes very great, and, of course, a constant supply of fresh air is required for the men themselves.

To supply this, air-compressing engines were worked upon the surface. Besides some smaller ones, which had been provided by the Great Western Railway Company before the contract was let to me, we had two double 20-inch air-compressors, and one double 16-inch air-compressor. One double 20-inch was worked at the main shaft at Sudbrook, one 20-inch at 5 miles 4 chains, and the 16-inch one at the Marsh Pit.

The air from the compressors was led to an air-receiver, a wrought-iron cylinder, something like a boiler, in which the air was maintained at a pressure of about 60 lbs. to the square inch. Under this pressure the air was so hot that it was hardly possible to bear the hand for any time upon the outside of the receiver. From the receiver wrought-iron steam-pipes, 2 or 3 inches in diameter, were led away to the various places where rock-drills or other machinery were to work.

As almost all the headings required blasting, the boring of the holes was done by machine-drills. Several patterns of these were used: principally