GraemeGTB wrote: ↑Thu Aug 05, 2021 11:15 amForget about using Propane, unless you've designed the gas tank to work at the much higher pressures reached by straight Propane. Flexible hoses also won't take the higher pressures. Commercial model tanks are designed for the working pressure of Butane at normal temperatures, or mixtures that are fairly low in Propane. The Material Safety Data Sheet (MSDS) for a given brand of gas mixture will tell you the composition of what is being supplied.Trevor Thompson wrote: ↑Wed Aug 04, 2021 2:35 pm So I think I need pure propane to get the full potential out of this loco.
The simplest way to use Butane in cold weather when the gas tank is remote from the cab, such as in the tender, is to locate it in a water bath filled with lukewarm water. Both my Shay and my Garratt have this arrangement and will run happily in very cold weather.
The maximum heat output of a gas burner is determined by the size of the jet and the pressure in the storage tank. Higher pressure and/or jet size result in higher gas flow and thus a higher combustion rate (and a higher consumption rate).
As a rough guide and averaged across a normal run, a standard Roundhouse burner will burn 0.6g/min of Butane and turn 5g/min of water into steam. I use those figures as the performance benchmark for my scratchbuilt locos.
Regards,
Graeme
The tank is very robust and I have tested it to 400 psi (an unofficial personal test of course). I have also experienced blocked jets using high propane content - so am confident that the gas resistant hose I am using will cope with the pressure. So a high propane mix doesn't concern me w.r.t. safety.
Thanks for the idea of a water bath - I didn't realise that was a workable solution. I had sort of wondered about it - but didn't know if it would work. I will see how I can implement that. I would be quite happy to use gas with low propane content - at least it is easier and cheaper to get hold of.
I put a larger jet in when working on a low propane mix, and then changed to a high propane mix without changing it back. I think I might be opening the gas valve too much and effectively having a blow torch flame hitting the smokebox without realising. It certainly raised steam quickly, but the front end did seem to get hotter than I expected - but that might explain why the gas pressure is dropping if I am using gas at an unnecessarily high rate. I am going to try it again this morning - with a no 6 jet - and I will run it with the firebox door open so I can inspect the flame and get a better feel for the level of roar which represents the correct flame.
Trevor