Garden Railway Forum

GTB wrote: ↑Thu Aug 05, 2021 11:15 am

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.

Forget 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.

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

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

Trevor Thompson wrote: ↑Fri Aug 06, 2021 10:04 am 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.

Poker burners and single flue boilers can be very sensitive to jet size. The burner I made for my Argyle Philadelphia only works properly with a particular size jet. Change the jet one size up and the boiler blows off continuously at the minimum setting, one size down and it never raises pressure. The operating range of gas burners only has a factor of two between minimum stable output and maximum output......

Flue length also comes into it and if the jet is too large the outer part of the flame can easily extend out of the flue. The free gas area through the chimney and bottom of the smokebox is also important to proper burner operation and adequate steaming capacity. It's not unknown for the paint to burn off the smokebox during a run if the burner/flue/smokebox proportions are out, even though the burner appears to be burning properly in the flue.

Then there's the issue of howling burners......... I make my scratchbuilt burners adjustable longitudinally, so if they howl when first tested, the resonance can be tuned out by moving the burner position in the tube.

Graeme

ps. A gas tank water bath doesn't have to be anything elaborate. It can be a simple open box made from thin brass and soft soldered together. If there are no electrics in the tender, it could just be the tender tank made leak proof.

Thanks for another detailed answer. I think I am beginning to understand better how it works. Obviously my first attempt at a single flue boiler with a poker burner.

I have fitted the no 8 jet in. The burner performs quite differently - still loads of heat but much easier to control. I was generating a flame thrower! The gas pressure isn't dropping either, and still loads of steam. I will try a water tank in due course but for now I want to keep it running!

With that larger jet it was all or nothing - and the smokebox was getting too hot. So were the cylinders. I was judging the valve setting by listening to the roar from the burner. Hence too much flame. With the smaller jet it still roars but with a lower gas flow. It is judging how much roar represents the right flame - especially outside. I know I can reduce the roar - the gauze covering does that - but I quite like to be able to hear the burner so that I know it is still lit.

Trevor

Trevor Thompson wrote: ↑Sat Aug 07, 2021 1:19 pm I think I am beginning to understand better how it works. Obviously my first attempt at a single flue boiler with a poker burner.

There's a reason why Brian Wilson and Paul Blake titled their AME article on burners 'The Black Art of Butane Burners'. The article was reprinted in Brian's book as part of chapter 11.

Sounds like you are now heading towards the Goldilock's zone for that burner/boiler system.......

The only article I've seen that discusses the design of butane burners in any detail is one by Paul Trevaskis, published in AME back in 1997.

Trevor Thompson wrote: ↑Sat Aug 07, 2021 1:19 pm With the smaller jet it still roars but with a lower gas flow. It is judging how much roar represents the right flame - especially outside. I know I can reduce the roar - the gauze covering does that - but I quite like to be able to hear the burner so that I know it is still lit.

I avoid using gauze if at all possible. It will make a burner quieter, but it also reduces burner output, as it restricts gas flow. Shouldn't be needed for burners that have rows of holes, as they are quieter than ones with slots.

All my gas valves are fitted with a handle that indicates the valve setting. A temporary expedient is to apply a line to the knob with a marking pen. You'll find that the minimum stable setting of most burners is with a valve opening of about 1/8 of a turn.

Graeme

Having spent a few days playing with this loco to get the hang of keeping the burner at the right burn rate, and learning how much to open the regulator with a heavy train I have a photo to share. It brings together the "Railway in the Valley of the Mill", the "quarrymen train" and this thread:
She pulls that load up a 1 in 60 slope easily, will accelerate with it, and pull it very slowly in a most satisfying way.

Trevor

I suppose I will have to paint her soon!

Wow, that is one heavy train!
Painting all those figures must have been a labour of love?

The painting did take a while! However most of it was done with an airbrush in batches, which does speed things up. It is a heavy train - 6 of the figures are made from modelling clay, and the rest from casting resin.

Trevor

Well I finally got around to painting Linda.

Partly dismantled, removed cab water tank coupling rods and smokebox. It took some cleaning to get all the oil off, but then etching primer:
And then high temperature black all over, and the green where the photo of the real thing showed it needed it such as the cab sides:
and of course the red lining, much easier to do when it is flat on the bench.

Trevor

Just the back of the tender to line, and then the garter crests to paint onto the tender sides. I didn't take the tender off because it meant undoing all of the servo wires, and the gas pipe. Perhaps the next time I make a tender loco I will add connectors so the tender comes off easily:
Trevor

A masterpiece. I really admire all the problem-solving and customization that went into this locomotive.

Keith S wrote: ↑Mon Nov 29, 2021 6:15 pm A masterpiece. I really admire all the problem-solving and customization that went into this locomotive.

Thanks - it feels good to have it almost finished.

Trevor

That is the crests finished and the tender lined:
The dust in the green paint isn't actually in the paint - I looked after taking the photo. I have now printed some name plates on the resin printer. I looked into etched brass ones, but the delivery and price sent me back to my own resources!
These have turned out better than I expected. So I will try makers plates which are a bit more difficult.

Trevor

Looks great!

Brass name and works plates from MDC in about six weeks, about £26 a pair, and they were matched to the full-size plates and look great.

To the best of my knowledge, other than when it was black (!), Linda has never had a black cab front. Blanche certainly did though, reminding us that FR locos are really black with a few green panels.

Also, other than for a short while when it ran with no tender, Linda's rear buffer beams (loco and tender) are black.

TonyW wrote: ↑Tue Nov 30, 2021 4:28 pm Looks great!

Brass name and works plates from MDC in about six weeks, about £26 a pair, and they were matched to the full-size plates and look great.

To the best of my knowledge, other than when it was black (!), Linda has never had a black cab front. Blanche certainly did though, reminding us that FR locos are really black with a few green panels.

Also, other than for a short while when it ran with no tender, Linda's rear buffer beams (loco and tender) are black.

Thanks for the feedback. The photo I downloaded made the cab front look black but when I look again I can see it is actually green. And the buffer beams are easy to alter!

Thanks again

Trevor

TonyW wrote: ↑Tue Nov 30, 2021 4:28 pm Looks great!

Brass name and works plates from MDC in about six weeks, about £26 a pair, and they were matched to the full-size plates and look great.

To the best of my knowledge, other than when it was black (!), Linda has never had a black cab front. Blanche certainly did though, reminding us that FR locos are really black with a few green panels.

Also, other than for a short while when it ran with no tender, Linda's rear buffer beams (loco and tender) are black.

That is the rear facing buffer beams painted black, and the cab front painted and lined:
I have also fitted my 3 D printed name plates and makers plates.

I know the lettering on the nameplates is bigger than on the original, and the chimney should be painted black. But there comes a point where it is a reasonable representation of the original, without becoming pedantic.

Trevor

Trevor it looks very good, but the most important thing is are YOU happy with it, if you are that is all that matters.

I agree with Jimmy, it does look very good. I'm impressed by the plates now they are painted. I thought they looked a bit bulky/heavy when straight off the printer, but the finished job looks excellent.

I saw this really lovely paint job on Linda when I visited the Railway in the Valley of the Mill before Christmas. She just looks superb. I had to ask if the plates were printed - and it only occurred to me to do so because I guessed Trevor would give that a go. You have to look very closely to tell.

Simon

Lovely photo - and thanks for all the kind comments.

I couldn't light the burner when Simon came round. Afterwords I looked to find why. It was just the burner had partly come out of the boiler. Pushed it back in and it lit first time!

Trevor

Well I was sorry not to see Linda steam over the viaduct in her new livery, but I am glad to hear it was a simple fix!