Page:Walker (1888) The Severn Tunnel.djvu/297

184 main. The pump-rods are of wrought-iron similar to those in the bucket-lift, and are guided at four equidistant points in the shaft by suitable guides, secured to strong iron girders built into the walls of the pit.

The suction and delivery valves are of gun-metal and of the four-beat type, as before described, seated in strong cast-iron valve-boxes, having windbores and bed-plates similar to those of the bucket-lift.

The pole-cases are mounted on, and secured to, a strong wrought-iron box-girder filled with concrete, and built into the walls of the pit.

The rising-main is of cast-iron 32 inches diameter, and in sections 9 feet long.

The flanges are all accurately faced, and those of the valve-boxes and pole-cases have a strong wrought-iron ring shrunk on them as an extra precaution against sudden shocks.

All pumps and valve-boxes, with valves in place, were tested by hydraulic pressure on the contractor’s works to upwards of four times the working load.

To supply the condensers with cold water, there are six 12-inch house-lifts in the 29 feet pit, worked by a set-off from the iron pump-rods, one to each engine. These are of the plunger type, and take their supply from the respective pump-heads of the rising-mains, and deliver same into the several condensing cisterns.

There are also two 12-inch fresh-water pumps in the same pit. They are worked off the 35-inch plunger-lifts by a set-off placed immediately over the plunger-pole, and they take their supply from a fresh-water spring, cut at or about the bottom of the well.

They are also of the plunger type, having gun-metal four-beat valves and cast-iron rising-mains, delivering fresh-water into a reservoir at the surface to supply the neighbourhood.

The pit is amply provided with various ladders and stages, affording easy access to all parts of the pump-work. The valve-boxes being all about the same level, and the most important part of the system, a