Large Gas Burner

[ptlrcecil]

Hi Guys
Im just finished setting up a large 0-8-0 freelance loco for a freind. The boiler is absoloutly massive 7" long by 2.5" diameter with a 3/4" centre flue. The purpose home made burner that came with it simply wont sustain a stable flame (The model has never turned a wheel) so Ive been testing it a standard Roundhouse FG type burner. However it simply cant churn out sufficient heat to keep the pressure up (light engine it goes from 80 psi to 15 psi in a matter of seconds. Wondered if anybody knew where I can source a larger burner to suit such a loco.
Cheers
Cecil.

[Sir haydn]

have you tried someone like maxitrack who are now gas firing the larger scales. they may be able to offer some ideas.

[GTB]

Im just finished setting up a large 0-8-0 freelance loco for a freind. The boiler is absoloutly massive 7" long by 2.5" diameter with a 3/4" centre flue.

Wondered if anybody knew where I can source a larger burner to suit such a loco.

What size are the cylinders compared to Roundhouse ones?

That boiler is about 50% bigger capacity than a Roundhouse Fowler boiler, but the centre flue dia. and length is much the same, which limits the size of burner that can be fitted to something the size of a Roundhouse one.

It sounds like the Roundhouse burner is getting the boiler up to pressure (how long though?), but the cylinders are using/leaking excessive steam, to drop the pressure that fast and the burner can't keep up. It's possible the valves haven't seated properly yet and are leaking a lot of steam.

If you are confident there are no cylinder steam leaks, you could try a larger jet in the Roundhouse burner. The burner can't go larger in dia., but it could possibly be made longer to give better combustion with a larger jet. Again there's a limit, as past a certain point the extra heat will just burn the paint off the smokebox and then go straight up the chimney.

There's a lot of black art involved in model loco gas burners. I was having similar problems with the burner that came with the loco, (which also thought it was a siren) and I built two new burners and tried three sizes of jet before it was sorted out. In the event, after 3 burners and 3 jets and a month of head scratching, I ended up with a nice quiet burner with a smaller jet, as the air/gas ratio has improved to give better combustion.

Can't help with suggested jet sizes, or sources, as Aust gas appliance jets have a different numbering system to UK ones.

Regards,
Graeme

[ptlrcecil]

Hiya. I tried some larger jets in the FG to no avail. I am starting ro think the boiler is flawed due to its size and lack of superheating. I've but the project on hold till I get clearance from the owner for a larger burner.

[Keith S]

I for one would like to see a photograph of this engine. Also around the web there are some discussions about burner building, it looks like it's tricky to get right but building one isn't necessarily difficult. maybe some kind of extra long radiant burner would work or perhaps some baffling in the flue?

[GTB]

Hiya. I tried some larger jets in the FG to no avail. I am starting ro think the boiler is flawed due to its size and lack of superheating. I've but the project on hold till I get clearance from the owner for a larger burner.

Probably means that the FG burner can't get any more air to make the extra gas burn properly. That, or the gas system is limiting the flow.

Running at 80psi is also expecting a lot from the burner, as the water temp at 80 is 40C higher than it is at 40psi.

Without seeing the chassis and boiler drawings and looking at the burner working, it's hard to make much in the way of useful suggestions.

I doubt the problem is just the boiler though. The cylinders must be very large, or very wasteful, to use steam that fast and I can't help thinking they are part of the problem.

Regards,
Graeme

[ptlrcecil]

Like I said its not superheated so the Roundhouse cylinders just sap the wet steam.

[GTB]

Like I said its not superheated so the Roundhouse cylinders just sap the wet steam.

Roundhouse cylinders are all the same size, even with different size boilers, so their standard burner should have no problem steaming a pair of their cylinders.

Is it possible to reroute the steam pipe and run it down the flue tube? Roundhouse burners are already set up for it and it might be easier than trying to make a larger burner work properly.

Graeme

[TonyW]

The boiler is absoloutly massive 7" long by 2.5" diameter ...

That sounds about the same size as an Accucraft Garratt or NG15 boiler. They got around this problem by fitting two burners.

You mention that the loco goes from 80psi to 15psi when running light engine in a matter of seconds. Most Roundhouse locos will run quite happily pulling a train on 15 to 20psi.

Could you tell us too why there is a need to run it at 80psi? Most coal-fired locos run at 60psi just to make the axle pump and blower more efficient, but it is not an absolute requirement and they will run on much less. 80psi will trash the cylinders in no time as it increases the pressure on the valves, so causing them to wear quicker. The piston and valve rod glands will also not last as long. In short, Roundhouse cylinders are not designed to take 80psi, so why the need?

BUT....

[GTB]

That sounds about the same size as an Accucraft Garratt or NG15 boiler. They got around this problem by fitting two burners.

Garratts have two sets of cylinders, so require twice the steam. From Accucraft's point of view it was probably easier to fit two standard burners than design a new burner with twice the heating capacity. Even assuming you could get a suitable gas jet that size.

If I was building a Garratt out of say two Roundhouse Billy chassis, I'd be working on the principle that the boiler would need two FG burners to steam four cylinders and would need twice the water volume to carry enough for a decent length run.

I just can't see how two cylinders could drain a boiler as fast as reported (I'm not doubting the report), especially as a larger boiler at higher pressure will have more stored energy. Even the safety valve sticking wide open would be hard pressed to drop the pressure any faster.

Graeme

[steamrocks]

I have built larger boilers for a G scale 2-4-4-2, and had the same problem with the FG burner, not enough fire to make the steam. What I did is to cut off the poker portion of the FG burner, leaving about a 3/4" 'stub' which has no burner holes in it. I took a piece of brass tubing that would just fit over this stub, cut to my new burner length, and silver soldered a cap onto one end. Using a dremmel tool with a cutoff wheel (the heavy duty ones) I cut slots at a 45 degree angle at about .2" intervals in the tube. The slots are about 1/3 the depth of the tube. This somewhat simulates a Pearse burner but the slots are at an angle decrease burner noise. Put this on the end of your Roundhouse burner, and you have an extended poker burner for large boilers.

You can make burners much longer than the original Roundhouse. The burner for my Mallet is over 3", approaching 4". Stay less than 1/2 the length of the flue. You will be surprised at what the added length does to boiler operation. You will need to experiment with length. Length of the burner will significantly change lighting and operating characteristics. You may only be able to light from the underside of the smokebox in some cases.

I originally tried the stock FG burner in my super boiler, and got exactly the same result as you did. Only after lengthening it did I get the steam recovery I required.

You might also want to get a #7 jet instead of the #6 that comes with the FG. You'll burn gas faster, but you have more of a boiler to fire, that's expected.

If you have your gas tank in the tender, I suggest a water bath around it. If you put in warm water, the gas pressure will rise. BE CAREFUL!! I use a hot water feed directly from the boiler with a shutoff valve, but extreme caution must be taken when attempting this. Do not take these comments as instructions to build such a system. High pressure gas is dangerous.

All this gave me a 2.5" x 9" boiler (not including smokebox) with a 3/4" flue that performed well feeding four Roundhouse cylinders.

The trick is in getting more fire area or length in the flue. The limit for operations I have found is something less than 1/2 the boiler length.

I just found out that this alteration does NOT work for the smaller diameter Pearse burners in 3/4" flues! Only the larger diameter Roundhouse FG burners work as a starting point for this enlarged burner in a 3/4" flue. A modified (lengthened) Pearse burner will work in a Pearse boiler with its smaller diameter flue, but NOT with a 3/4" flue. You will NOT get the steam recovery you need.

I have also gone the other direction: a smaller diameter flue in a tiny 1.5" diameter "T" boiler for a 14 ton Shay. I did not use a Roundhouse FG for this, but scratchbuilt my own based on FG dimensions.

One closing thought: To test your firing system without building a boiler, simply 'mock up' just the flue you are going to use at the length you are going to use it. In your case a piece of 3/4" copper tube the length of your boiler (not including firebox). Mount the test burner in the tube, light it and observe operation. This will get REALLY HOT and the test flue will probably eventually anneal and/or collapse, but it will stay alive long enough to test your burners. With the open exposed test flue, there is no surrounding water to cool it. Initial start-up performance with a real boiler may vary because the surrounding cold water keeps flue temperaature down for a while. Start off with a very low gas regulatur setting. Another warning: these longer burners WILL consume gas faster for a given flame intensity.

[JMORG]

Add a Ceramic burner! Superior to the FG burner in every way in my opinion: Quieter, easier on fuel, and produces ALOT more heat!
Forest Classics is the company that sells them.