Engineering Wonders of the World
Volume III

GREAT BRITISH DAMS AND AQUEDUCTS. 187 SKETCH MAP SHOWING COURSE OF THE THIRLMERE - MAN- CHESTER AQUEDUCT. safeguard is provided by valves which auto- matically cut off the supply in the event of a rupture. In a paper read before the Insti- tution of Civil Engineers, Mr. G. H. Hill, M.Inst.C.E., describes the mechanisms of this class which protect the Thirlmere Aqueduct. At the north—that is, the upper—end of each syphon is a chamber divided trans- versely by a wall. The southern part of the chamber is subdivided by partitions into a number of float wells, one for each of the pipe lines of which the syphon will ultimately be made up. The north compartment lias com- munication with each, float chamber through a pipe, the ends of which, are turned up so that the lips are horizontal. Over the northern orifice of the pipe a bell-shaped vessel, open end downwards, is suspended from a lever 18 feet long pivoted at the northern end, and carrying at the other a large metal float. Should a burst occur in the syphon pipe the water in the corresponding float well sinks, and allows the bell in the northern chamber to seat itself over the entrance to the com- munication pipe, and so cut off the supply. Any excess of water from the aqueduct is discharged through a channel at a level below the top of the cross wall. pipes apart. In some cases a wrought - iron ring is shrunk over the socket to assist in pre- venting fracture during caulking. In moderately flat country cy- lindrical socket- less pipes, joined by collars em- bracing the ad- jacent ends of two pipes, are used. For nego- tiating horizon- tal or vertical angles and curves special angle castings become necessary. On severe slopes pipes must be anchored to pre- vent downhill movement, and be duly supported on the outside of curves against outward thrust. In this country it is customary to cover water-pipes with at least 2| feet of earth as protection against that arch-enemy of the hydraulic engineer, Jack Frost. However carefully a syphon may be de- signed and laid, there is always the possibility of a burst occurring in it. Were such a vast volume of water as is carried Valves^æ by a ^a,rge aqueduct allowed to escape unchecked, the re- sults, apart from the great waste, might be disastrous. A syphon is therefore furnished with a number of valves, under the control of the walksmen who patrol the line, whereby an outburst may be restrained. A further Another type of automatic valve is fitted at intermediate points in the northern legs of the longer syphons. A disc valve, which, when turned into a vertical position, seals the waterway, is carried on trunnions project- Automatic Throttle Valve. ing through stuffing boxes in the sides of the valve box. On the ends of the trunnions are pulleys, to which heavy weights are attached by chains. Under ordinary conditions the valve lies in a horizontal position, allowing the water to pass at its normal velocity. Upstream of the valve a circular plate, on the end of a rod pivoted in an air chamber above the valve box, projects into the water- way. Should a burst occur, the increased velocity and pressure of the water causes this»