This is part of a tank that sits just in front of the driver's cab on the Fowler 0-6-0 steam engine that can be found outside Erwood Station Arts Centre.
I'm not sure what it does, and a quick Google search shows many similar engines without this feature. Most curious.
For myself, I just love the texture in this shot. It'll make a great wallpaper, especially if you put your desktop icons on the left of your screen.