Follow these links for pics of (similar modern equivalent) gauges on a fire engine's fire control panel:
http://static.howstuffworks.com/gif/fir ... -panel.jpg
You can see now why the "lip" on the gauge is there, to make it sit flush and correctly within a panel not unlike this one.
And another:
http://wwwdelivery.superstock.com/WI/22 ... 430291.jpg
Another:
http://www.istockphoto.com/file_thumbvi ... gauges.jpg
Images of fire tender delivery system panels are hard to find. I am still to find the "holy grail" pic that shows Dobros gauges fitted, but I will keep looking and focus all further research in this direction. I am confident I will turn up something...perhaps another one or two gauge assemblies.
Please note on the images in the links the gauges go up to 400 and even 600 psi, which are super high pump pressures. The Mad Max gauge face has increments of 50...up to a total of 250 (psi originally) this could add further credibility as fire appliances in the 70's and 80's likely had a max main pump pressure of 250psi. Also there are lots of other variable factors...pump size, hose outlet quantities, appliance capacity, hose bore etc...
Definately more research to be done.
The original 100mm lipped Dobros gauge I am certain possibly was a main pump discharge gauge on a fire engine, this may have been it's application and design function. Exactly what make and model fire engine(s) I have yet to determine. I will advise new developments as they come to light...(time to interrogate my uncle who has spent 40+ years in the NZ fire service, and maintained/crewed many makes and models of appliance).
I am convinced that this is the right place to hunt down these elusive items. Anywhere who fits out fire engines,tender wrecking yards, fire equipment auctions etc...
This is why they have not been tracked down, because no-one yet has properly identified the original use and application of these gauges.