Errol,
A pressure regulator is indeed the way to go for a T/G running on variable steam pressure. I use one on my 3.5" gauge locomotive and it functions well.
Building a reliable pressure regulator that small is not a trivial pursuit... I have designed and built several. If you want a set-and-forget type of regulator of reasonably small size, in my case the regulator is roughly the size of the T/G, a metallic, convoluted, diaphragm is necessary to keep the hysteresis to a minimum. Flat diaphragms in metal don't work because they stretch and introduce an "oilcanning" effect. If you can lay your hands on a thin piece of fibreglass reinforced teflon sheet, say .010" or so thick, that might simplify things. The diaphragm has to withstand the full steam pressure and temperature.
My diaphragms are .003" thick bronze sheet with one convolution formed in a die with a urethane pressure pad. The finished disk is 3/4" in diameter. Stops need to be built into the unit to prevent excessive movement when the steam is off and the spring exerts its full force; ditto when the steam pressure is at a maximum and the spring is relaxed by withdrawing the adjusting screw.
In the 1950's Model Engineer described a number of these devices... I was not impressed by them because I wanted a set-and-forget unit. But they did form the basis for the thinking process.
If you wish to pursue this let me know and I will dig out the magazine number. Unfortunately my design exists only as back-of-envelope sketches, not suitable for publication. If there is some interest I could perhaps get CAD drawings made and supply these at a moderate cost.
Arminius
