The SWIVEL BRIDGE is Brunel's first large wrought iron opening bridge, it is far older than the Suspension Bridge, and is Bristol's only abandoned Brunel structure. The Bridge is listed Grade 2* and is on English Heritage's Buildings at Risk Register. The bridge rotates on four fixed wheels in contact with a solid ring under the bridge. The bridge was turned by a hydraulic mechanism of twin rams located in pits that are connected to a turning ring under the bridge via a substantial wire cable. The original turning mechanism prior to conversion to hydraulic machinery was a hand turned crank similar to that used on old train turntables. The pistons and chains are still in position. The original hydraulic system ran on fresh water supplied from a pressurised water system sited in Underfall Yard.