Page:Walker (1888) The Severn Tunnel.djvu/163

94 The only thing necessary was to make this self-acting, and this was done by Mr. Schenk in a very ingenious manner. A small wooden box, divided into two compartments, was fixed to rock on a centre at the top of the shaft, and a small pipe led to discharge directly over its centre. When this small pipe filled the one compartment of the box, so that it was heavier than the other, the box turned upon its centre-pins, and in doing so opened a valve on the air-main by means of rods attached to it, and allowed the compressed air to pass into the tank and force the water out of it to the surface. The small pipe then filled the other compartment of the box, and reversed the action, so that the pump was made perfectly self-acting, and required no looking after. These pumps were used throughout the period we were lowering the heading, and proved a complete success; and afterwards, when we had rather more water at the Marsh Pit than three 15-inch pumps could master, I fixed one of them there to lift water to a height of 100 feet. It was as perfect a success, lifting water 100 feet as it had been lifting 25 feet.

Of course, working by compressed air in this manner is expensive; but underground, on account of the difficulty of ventilation and the heat, it is necessary in many places to adopt compressed air for working machinery. Electricity could be used for the same purposes, but I have only used the compressed air, and that I have used for winding by steam-crabs, for pumping, and working rock-drills.