Written 2009 in response to an email query.
Our track has 2 1/2", 3 1/2", 5" and 7 1/4" gauges available. There are five sets of points, four of which are actuated with hydraulic rams using mains water pressure. The fifth one is manually operated. This gives us a main line past the steaming bays with a separate road into the steaming bays, two roads through the station and a back shunt.
The photo below shows the track arrangement. The outside rails are for 7¼". The next pair in from each side are for 5". The near two rails are 1¼" between inside faces, the far two 1" between inside faces (which allows the 2½" gauge by using that rail and the centre rail). The 5" rails are therefore offset slightly. The centre rail (¼" thick) gives 3½" to each of the outside rails.
The diagram shows the critical dimensions.
The under frame is a light truss.The section of track that is free of the under frame allows the rail for float to its own natural curve. Under the chequer plate in the foreground is the hydraulic cylinder and actuating arm.
This is a not very clear view of the pivot. The conduit is to carry wires to the position sensor to activate the signal lights.
Looking down on the pivot. Note that the tracks, free of the under frame, have floated off centre.
This shows (one of) the wheels that provide lateral stability at the free end. There is a substantial stop welded onto the end of the outside rail to limit travel.
The next two photos show the slip joints that allow the track length to move to cope with the curve. Note that the slip joint is at one end of the floating section of track. The 'sleepers' in the floating section are notched to allow the tracks to move end ways but still maintain their gauge. I think the sleepers are welded to the centre rail. Sleepers are at 300mm centres. The slip joint and the next sleeper to the right (out of shot) are attached to the under frame so there is no bending at the slip joint. Visible in the near track on the lower photo is the slot with loose rivet that keeps the two parts of the track together.
The next three photos show the points operating mechanism - full size levers actuating ball valves to deliver mains water to each end of the hydraulic cylinder that moves the points. Hydraulic in this sense is the use of water as the actuating fluid. Although we have frosts in the winter it never seems to get cold enough to freeze the pipes underground.