Hawarden Swing Bridge
1884 The Manchester, Sheffield and Lincolnshire Railway initiated the scheme to design and build a bridge across the River Dee at Shotton, west of Chester.
1887-9 Bridge constructed. The Engineer for the project was Francis Fox, M. Inst. C.E. The main contractors were J. Cochrane and Sons, and the steelwork and hydraulic and mechanical systems were subcontracted to the Horseley Co. The bridge had three spans, one of which opened to allow river traffic.
On 11 August 16th, 1887, the ceremony of lowering the first cylinder of the new bridge was performed by the Right Hon. W. E. Gladstone, M.P. The bridge was formally opened to traffic on 3 August, and named Hawarden Bridge, by Mrs. Gladstone. The Gladstone family estate was at Hawarden Castle, a few miles to the south of the bridge.
The swing span was the longest in the UK at the time, having a length of 287 ft. and a clear opening of 140 ft. The swing girders are 32ft. deep at the centre and 9ft. at the ends. The top and bottom members are 2ft. 6in. square. The girders of the fixed spans are 134 ft. long and 20ft. deep at the centre.
The bridge was swung hydraulically, using water at 700 psi. The engine house/look-out tower (the roof and chimney of which are just visible in the first engraving) contained two steam pumping engines, three boilers, and two accumulators. The system supplied two horizontal rams, one on either side of the pier. A pitch chain is connected with the piston of each side rams, and carried over pulleys fixed to the ends of the pistons to a sheave, by which the bridge was swung. The one ram pressing out, swung the bridge, and drew back the other at the same time. When the bridge was to be opened for navigation it was raised, and the solid bearing blocks drawn back by hand through shafting connected with the spoke wheel in the look·out room. The bridge being free, the tail end - which was on rollers 7 in. lower than the centre bearing when across the opening - was gradually lowered, and began to move slowly at first along the tail race. When the bridge was brought back to position the tail was raised by means of two rams, so depressing the end into a tapered recess and lifting the tail into another tapered recess, thus bringing the rails truly in line. The bearing blocks were then run in by hand wheel, and the bridge was locked. The time required to remove the bearing blocks, lock the signals, and open the bridge, was about two minutes. [1]
Immediately north of the bridge is Hawarden Bridge Station, opened in 1924 to serve the John Summers and Sons Shotton Iron and Steel Works, located on a large site immediately north west of the bridge.
In the 1960s the swing mechanism was taken out of service and the bridge fixed in position. The control tower was demolished in the 1980s.
A pedestrian/cyclist walkway carries the Chester Millenium Greeenway across the bridge.
See here for more information about the bridge in the broader context of the railway and river traffic.
More information here, including weights of swing bridge components.
The design and construction of the bridge were described and illustrated by Francis Fox in an I.C.E. Paper, 'The Hawarden Bridge'. This provides the following additional information:-
The steam pumping engines were made by Frank Pearn and Co. Frank Pearn also designed a valve which provided delicate control of the rate at which water was admitted to and released from the main hydraulic rams. This features a form of sleeve with sixty 1/8" diameter holes which were covered and uncovered by a sliding piston valve.
The swing bridge revolved on a spherically-seated bearing located in the top of a cast iron pillar. The bearing was periodically lubricated with heavy oil. The upper part of the bearing was located in a large forged steel crosshead, attached to the bridge by two 9" diameter bolts (see photo). The bolt threads are of the buttress type.
See Also
Sources of Information
- ↑ The Engineer, 29 Nov 1889