Fit and forget bearings be dammed

There are less things for hydro engineers to worry about when designing dams, thanks to Vesconite


Vesconite bearings have been used in the control arm linkages on the radial deep sluice gates for a hydropower dam on the Nile River. The project began seven years ago, but another dam, this one in South Africa, is nearing completion also uses Vesconite bearings. In this case, the company's Hilube trunnion bearings which can be found on the tainter gates at the Kruisvallei Hydro Power Plant on the Ash River. Vesonite states that the 'no-creep' characteristic exhibited by its material makes it particularly sought after in these hydro applications because the bearings are fully statically loaded to cope with the significant water load bringing large applied stresses.

The company says that another attribute valued by the designers of these dams is that in hydroelectric applications, Vesonite Hilube bearings are swell resistant,  with a confirmed negligible 0.13% mass change after 28 days of being fully immersed. Vesconite also doesn’t soften under these saturated conditions, hence its resistance to creep.  “The radial arm sluice gates that will be installed at Kruisvallei, and the associated trunnion bearings, which are located at the pivot point that allows for the movement of the gates to release or stop water flow, are a vital part of the project”  says Wicus Bonnett of contractors Eigenbau. “They will be open most of the time - about 90% of the year,” he says of the gates. They comprise two intake, two tailrace and two emergency gates - one of each per plant.

An operating flow of 37m3/s must be stopped and released during maintenance and emergency shutdowns, which is likely to take place between four and six times a  year. In addition, flow may also need to be stopped to protect against 1 in 200 year flooding risk, to safeguard the hydro electro-mechanical equipment that could be damaged in such a situation. Similarly, for the North African project, some eight bushes were installed on five 9.5m control arm linkages that link hydraulic cylinders to dam gates that are used to control the water flow along this part of the Nile River. These were important since the linkage arms connect the sluice gate to the hydraulic cylinder and allow the gates to be lowered or raised with the water on the Nile. This allows for optimal water volumes in the dam, which would otherwise risk being breached if the flood waters were not controlled sufficiently. 

Besides low-creep and no-swell, other advantages of Vesconite Hilube bearings in hydroelectric applications are that they can be manufactured to any dimensions, which makes designing easier; they have a high load-bearing strength, so there may be a cost saving on bearing design since bearings can be made more compact while withstanding the force of the water; they have a low coefficient of friction, which minimises the forces on the structure during operation; and they are self lubricating, so they will not seize despite being stationary for long periods. 



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