Acton Bridge Swing Bridge carries the A49 across the River Weaver, near the village of Acton Bridge in Cheshire.
First operated in 1933. It has been subject to periodic strengthening.
Sometimes erroneously described as the first floating swing bridge in Britain.
It is a steel bowstring truss balanced swing bridge, 83.5 m long, 8 m high, swivelling on a concrete base which is also a caisson for the pontoon (the buoyancy cylinder). The 'pontoon' is a riveted cylindrical steel tank attached to the underside of the bridge, contained within the cylindrical concrete caisson which supports the roller ring. The cylindrical tank is 35 ft diameter, with a convex floor. It is hidden within the water-filled chamber of the concrete caisson, whose inside diameter is 40 ft and the depth about 27 ft.
The bridge was designed by John Arthur Saner. Steelwork by John Park and Son of Northwich.
It was the last of the large swing bridges designed by Saner. His other swing bridges which carry major roads are:-
The present swing bridge is a short distance downstream of the first crossing of the River Weaver. A bridge was built to cross the Weaver at this point in 1751. A swing bridge was added to cross the new cut. The old swing bridge has been removed, while a handsome masonry skew bridge still crosses the old river course (see photo).
An illustrated description of the bridge appeared in Engineering in 1934 [1]. 'The slewing winch consists of a drum carrying two wire ropes each 1 3/4 in. diameter, which pass round the circular girder upon which the upper roller path is fixed. The ropes wind and unwind in a spiral groove chased on the drum, so that the bridge is always under control. The drum is driven through worm gearing attached to a 40-h.p. electric motor. An important factor is the application of the brakes, which have to be controlled from the distant cabin. Although the 40-h.p. electric motor is amply sufficient to slew the bridge, it does not represent the maximum load which is occasioned in the event of the bridge, when moving at the maximum speed, being suddenly pulled up on account of some vessel getting too near or other similar accidental cause. For this reason the brakes must not be applied too suddenly, otherwise there is danger of breaking the ropes, which will withstand a load of 120 tons only, and it was thought that the action of a solenoid might be too sudden. To overcome this difficulty, two brake sheaves, ... are fixed on the first motion shaft of the winch, and the bands are operated through screw gearing by two 5-h.p. motors, which are controlled by means of push buttons, and a set of contactors fixed in the control cabin ; these push buttons are within easy reach of the operator, and by their means either or both the brakes can be applied or released. A contact breaker is arranged to cut off the 5-h.p. motor at the end of the stroke, and each machine has a small solenoid brake, which, immediately the current is off, stops the armature revolving. So far this system of braking has been successful, and it is evident that the arrangement lends itself to application for purposes where the solenoid coil is too rapid in action, as, for instance, the slewing action of a large crane, where, with a load swinging at the end of a long chain or rope, the sudden stoppage of the jib is undesirable. When the bridge is across the river the ends When the bridge is across the river the ends of the girders are supported by electrically operated wedges. These wedges, together with the motor, screwgear, &c., are mounted on a continuous girder placed on the concrete abutment at each end of the bridge. When the wedges are withdrawn, the ends of the bridge are quite free, but until they are withdrawn, it is not possible to switch on the slewing motor; vice versa, when the wedges are down they can be raised again only when the bridge is in position and the slewing motor is no longer required. The arrangement of these is shown in Figs. 11 to 15 [not included here], the motor and alternative hand gear being underneath the supporting girder, and the motion being transmitted to the wedges by vertical shaft, bevels, screws and links. The transmission is of the spiral bevel type, the wheels being hardened by the Shorter process. It will be noticed that the links connecting the travelling gunmetal nuts on the horizontal screws with the wedges are slotted. This allows the motor to start without load, which comes on only when the nut has travelled the length of the slot and the motor has had time to develop its power. This form of slotted link connection was adopted for the smaller electrically-operated swing bridges at Northwich, which were erected under Colonel Saner’s supervision in 1899. These are still working satisfactorily, and, except for the occasional renewal of the gunmetal nuts and pin connections, have not given any trouble. A limit switch is arranged to prevent the wedges being over-run, and the buffer springs .... come into operation if the switch should fail. The wedges do not lift the bridge ; they are merely driven firmly home and held there by the links and travelling nuts. The thrust of the screws is taken by collars working in plain thrust blocks, the collars and screw shaft being machined from a solid bar. ..... The work involved in the foundations and pontoon chamber, piling, etc., was carried out by the Weaver Navigation staff, the contractors for the superstructure and machinery being Messrs. Joseph Parks and Son, Wadebrook Steelworks, Northwich.....'[2]
See also Wikipedia entry.