Page:Walker (1888) The Severn Tunnel.djvu/162

Rh When the machine-drills were being worked by compressed air in any of the headings, the air, after passing through the drills, kept up efficient ventilation.

We afterwards applied this compressed air to the pumping. When we were sinking the drainage- heading, 20 feet below the old workings, it was done from a number of small shafts sunk to a depth of about 25 feet from the old heading; and to pump the water from the lower level I adopted a pump which was designed by Mr. A. O. Schenk, and which proved to be thoroughly efficient. The pump consisted of a wrought-iron closed tank of any suitable dimensions, say about 3 feet square. A 6-inch wrought-iron pipe, passing from near the bottom through the top of the tank, was led up to the level at which the water was to be delivered. A 1½-inch wrought-iron pipe was connected from the compressed air-main to the top of the tank. At the side of the tank, near the bottom, several flap-valves were fixed, opening inwards.

The tank was then lowered into the bottom of the shaft, which was 4 or 5 feet below the level of the bottom heading, and the connection with the air- pipe was made. The water flowed into the tank through the flap-valves till the tank was full; the pressure of the air being then admitted at the top of the tank, it closed the flap-valves and forced the water up the 6-inch pipe to the required level; when the tank was empty the air-pressure was turned off, and the tank filled itself again.