Douglas Harbour - Swing Bridge
Built in 1895 by Sir W. G. Armstrong-Mitchel and Co Ltd of Newcastle upon Tyne, the Birdge which weighs 450 tons, is 24 feet wide, 118 feet from pivot to nose and 58 feet from pivot to tail. Originally operated as a toll bridge for vehicular traffic of up to 2 tons weight and pedestrian traffic, the toll was dispensed with in 1952 and the Bridge barred to vehicular traffic in 1959.
The engine house has to be staffed to operate the Bridge for all tide periods, or part thereof, from half flood to half ebb, which occur between the hours of 6am and midnight during the summer, and 7am to 11pm during the winter. In addition, the Bridge has to be “swung on” in the early morning and “swung off” at night when the limiting hours do not fall within a tide period.
The Bridge is hydraulically operated, the force-pumps being driven originally by a gas combustion engine with manual stop and start, are now driven by a 15hp electric motor. However, if an electric power failure occurs the force-pumps can be driven by a “Ruston and Hornsby” diesel engine, which is started and stopped by hand. In the event of failure of the hydraulic system the Bridge can be manually wound-off by use of the capstans situated on each side of the slewing area; manual operation requiring a gang of five men – four on the capstan and one tending the rope.
The hydraulic system which operates at 700 1bs per square inch and has been tested to 1,400 1bs per square inch incorporates an accumulator which maintains a quantity of water under constant high pressure – sufficient water to fully open, then fully close, and then fully open the Bridge again before the force-pumps have to be re-started. It is this water, when released through the control valves, that floods one of two slewing cylinders, both of whose operating-rams are connected by 128 feet long by 51/8 circumference steel wire ropes, to the Bridge through tunnels under the road. The slewing-ram selected extends pulling the Bridge with it and opening the Inner-harbour to shipping. The second cylinder is then flooded to pull the Bridge back, closing off Inner-harbour.
When the Bridge is across the harbour hydraulically operated wedges are inserted to lock the Bridge in place. This wedging gear receives its pressure from the accumulator through a control valve, and like the slewing-rams is operated manually from the Control Cabin.
| DisabledGo Information |  | Terms & Conditions | ©2008 Isle of Man Government |