Page:Walker (1888) The Severn Tunnel.djvu/97

42 bottom. The cause of the failure of the pump was then seen. The valves, both bottom valve and top valve, were of a new patent construction, called ‘Hat-band Valves.’ They consisted of a series of steps bored with a large number of ½-inch circular holes, and each step covered with a band of rubber ¾-inch thick; the principle being that the pressure of the water through these holes should expand the rubber, and find an escape for itself as the engine made its stroke, and close again over the holes as soon as the pressure was relieved.

It became manifest that these rubber-bands had offered a very great resistance to the passage of the water; and when the water was lowered to within 10 feet of the bottom of the shaft, the column of water standing nearly 180 feet in the rising-main above the bottom valve, the moment the bucket-valve began to make its downward stroke, the water not escaping freely through the bands of rubber, increased the already enormous pressure upon the taper-seating of the bottom valve, split the valve-case, and drove the bottom valve into the wind-bore. The engine thus released, ran out with great force; the column of water in the rising-main following. Unfortunately the bucket-rods were attached to the bucket without key or nut, but by a taper in the end of the rod, identical with the taper in the bottom valve below.

The shock of the water on the return-stroke of the engine tore the rod through this taper, splitting