Barry Docks: Bridges
The complex infrastructure of Barry Docks included a swing bridge and two sliding (retractable) bridges survives. Large retractable bridges are rare, and one of the Barry Docks survives as a listed structure, along with its control cabin. [1]. The cabin is in very delapidated condition, while the bridge is suffering from corrosion (2019).
See photo above and here.
The bridge was traversed by wire ropes actuated by two hydraulic 'jiggers'. The arranagement of ropes and chains served to multiply the travel of hydraulic ram. In this case each ram had four pairs of pulleys. 2007 photo here.
Photo here shows a pair of rollers and the supporting structure. This photo shows a bridge rail outboard of the support structure.
Photo here shows a device which presumably acted to shut off the hydraulic supply to the rams at the outward end of the bridge's travel. Judging by the fractured casting, it wasn't always successful.
More photos and information via this link. The bridge was constructed in 1889 by the Darlington Wagon & Engineering Co Ltd. Photo of builder's plate and counterweights here.