THE new Gulmarn lifting bridge at the V&A Waterfront forms part of the Marina residential development currently under construction. The bascule type bridge stretches across the 20m upper basin canal, connecting the south and north sides of the Marine. The bridge will provide pedestrians and club-car access across the canal and with the touch of a button; it can be lifted out of the way to allow yachts and other small leisure craft through.
Hyflo Southern Africa, the largest hydraulic company in the Western Cape with its many years of experience in hydraulic system design was the obvious choice for undertaking the design, manufacture and supply of the hydraulic system moving the structural steel bridge.
The bridge is pivoted on the northern side of the canal. One large, trunnion mounted, hydraulic cylinder below the fixed ramp is connected to the counterweight on the bridge. The bridge lifts through 90 degrees in 60 seconds. At the bridge tip another hydraulic cylinder locks the bridge in the down position.
With the required 50 years life expectancy of the system, Hyflo, who has recently entered into a distribution agreement with German cylinder manufacturer Hunger Hydraulik, used a special cylinder rod coating for the application. The Hunger P.T.A. coating, a first in South Africa, was specifically developed for piston rods operating in the extremely corrosive salt laden environments of the offshore field.
The P.T.A. layer provides full corrosion resistance to salt water, prevents salt water ingression through to the base material. Furthermore, local mechanical damage can be repaired in situ. The P.T.A. layer has a hardness of 43 HRC with a honed and polished surface finish of Ra<O.1 providing good wear resistance and low friction properties for stick-slip free operation. A new EVD sealing system is also incorporated into the cylinder. For the first time it is possible to compensate for seal wear without the need for replacing the seal.
The sequence of operations to open and close the bridge is automated using a PLC based control system. The sequence will be triggered with a wireless remote control unit. In addition to the remote control it is also possible to operate the system manually.
In order to move the bridge smoothly with wind loads up to 2 tons, Hyflo used the latest proportional hydraulic technology in combination with integrated manifold block circuit design. The manifold block is mounted directly on the cylinders in order to improve the overall rigidity of the system and bridge.