Fire arch design for propane

[Chris Hollands]

I'm in the process of looking at the fire arch for the challenger is there any design measurements that should be used or is it suck it and see .
The firebox is about 24 + 14 with a multi hole burner .
Also how thick should the arch material be etc.

[ccvstmr]

Chris...can only offer some comments and "general" rules of thumb.

1) arch sheet to extend nominally 2/3 to 3/4 way back into the firebox.
2) vertical opening from the arch to the crown sheet should be approx. 10% of the grate area.
3) leave some space behind the rear flue sheet to the arch so exhaust gasses can get to all the flues.
4) if you're burning coal...see if you can make a removable crown sheet design.
5) if you're burning propane...fabricate and install turbulators in each flue pipe (stainless steel suggested). If you're sheering the stainless, round the edges before twisting so the turbulator doesn't bounce and cut into the (assumed) copper flues.
6) check the Chaski archives. There's been several posts about the design, fabrication and use of arch sheets.

Hope that helps. Carl B.

[Marty_Knox]

The area over the arch should be 110-120% of the net area through the tubes, with 115% preferred. This is from the Revised Master Mechanics Locomotive Front End Arrangement from 1936. Note that they base it on the net area through the tubes and flues - not the grate area.

[Fender]

4) if you're burning coal...see if you can make a removable crown sheet design.

Removable crown sheet, or removable arch?

[Chris Hollands]

Thanks for the reply's Carl and Marty ,I did look at a few previous posts but they generally did not have a reference to how to size the arch .

The burner is monster rated at 300 000 btu @ 3 psi designed by Al Von Rubin In Seattle this is the biggest he had ever made and was using it to heat his workshop at one stage just to test it before he sent it to me .

What thickness material would be best , I was thinking 3/16 - 1/4" SS not sure how easy a small piece of 1/4" SS is to get .

[Marty_Knox]

Chris, I usually use 3/8" x 2" 316 SS bars run across the firebox. I get it from McMaster Carr. I will see if I have a picture.
That is the size I use with coal, burning propane you may be able to use thinner material.

[Chris Hollands]

Thanks Marty a picture would be great better than trying to explain , that material is quite easy to get from local metal suppliers .

For people on the west coast Alaskan Copper & Brass is a great source for this type of stuff - copper-brass-bronze-SS-Aluminum .

Down side $250 min purchase which does not take much these days .

[Bill Shields]

Find a fab shop and go dumpster diving...the pieces you need end up on the floor.

Start at a place that does water jet or plasma cutting. My neighbor works at such a shop and literally has a garage full of 'drops' that were going into the scrap bin

That's a big burner. Hope you can turn it down to idle.

I have 100000 BTU of burners in my loco and almost never turn on more than half of them at 50% rated pressure.

Problem i have is at the fully rated output it is tough to move that much air through the flues and out the stack so it becomes a delicate balancing act. Once I figured it out it is great.

Went through 4 arch iterations (slow learner).

Found that the recommendations for coal do not always strictly apply to propane (first two iterations). They are a good place to start but I eventually found better through trial and error.

Used something like 10 gauge thick sheet which seems to be holding up just fine.

[Marty_Knox]

Here is an arch in the G-5 boiler. Two with the bars in place, one without showing the supports.

[Berkman]

With coal do you actually notice a performance/steaming increase? or does it just reduce flu clogging

[ccvstmr]

4) if you're burning coal...see if you can make a removable crown sheet design.

Removable crown sheet, or removable arch?

You're right Dan...was thinking "arch", but accidentally wrote "crown sheet". However, if you think about it for a moment, a removable/replaceable crown sheet isn't such a bad idea. May not be practical...but would keep locos on the rail longer. Carl B.

[Chris Hollands]

Marty thanks for the photos , the arch looks quite small if that is 2" SS flat bar .

Bill - Al Von Ruben designed quite a few Propane burners on the west coast here and from what I have heard they are very successful , time will tell I guess .
The burner is rated at 1 psi per 100000 btu and is about 24" + 14" - 1300 burner holes ( Glad I didn't drill them )