Crown Sheet Height

[steam4ian]

G'day Matt

Fred has said some of what I would have said. I have just under 1.5" freeboard on my 5" gauge loco and it is not really enough because the barrel reduces to 4" diameter. You need to allow about an inch, even more for a long boiler, for gradient changes and the water level rise when you open the regulator (throttle). You can see that opening the throttle on a rising gradient doesn't leave much steam space.

Work out the number and diameter of tubes and flues you need using the spread sheet on John Baguley's web site then set them out. Make the firebox crown as low as you can.

Don't ask me how I found how important it is, even though the boiler inspector says it wasn't my fault.

Regards
Ian

[PRR 5741]

Hi everyone,
First off, I'd like to thank everyone for their invaluable assistance on the boiler for my G5s. I've been doing a great deal of corrective work on the drawings that I have, and I think the improved design conforms more closely to what a model design should be in terms of where the crown sheet should be, as well as a more realistic tube and flue layout. I'll attach a photo or two, but I'd really like to be able to attach CAD files if that's even possible. Back to the boiler, there is now 3 and 3/16 inches of space above the top of the crown sheet, 21 flues 7/8 inches o.d. and 24 tubes 3/8 o.d.

Safe Steaming,
Matt T.

[tsph6500]

21 flues 7/8 inches o.d. and 24 tubes 3/8 o.d.

Will there be superheater elements in the 7/8-in flues?

[kenrinc]

Will there be superheater elements in the 7/8-in flues?

That's what the drawing shows....

I'd really like to be able to attach CAD files if that's even possible.

I'd think that would be of little value to most of us here. Nearly every CAD app allows for export to PDF and if they don't it's easily done with other utilities.

Ken-

[Fred_V]

this forum won't accept DWG or DXF files but you can trick it by changing the suffix to DOC and it will come through OK.

[Fred_V]

Hi everyone,
First off, I'd like to thank everyone for their invaluable assistance on the boiler for my G5s. I've been doing a great deal of corrective work on the drawings that I have, and I think the improved design conforms more closely to what a model design should be in terms of where the crown sheet should be, as well as a more realistic tube and flue layout. I'll attach a photo or two, but I'd really like to be able to attach CAD files if that's even possible. Back to the boiler, there is now 3 and 3/16 inches of space above the top of the crown sheet, 21 flues 7/8 inches o.d. and 24 tubes 3/8 o.d.

Safe Steaming,
Matt T.

the 3/8" OD flues will accomplish absolutely nothing in a model. if you are trying to build a museum quality replica engine that's one thing. if you want to build an engine that will run on track that's something else. just use 3/4 OD X 5/8 ID flues through out. to make one of these run right you have to compromise in some places.

[tsph6500]

That's what the drawing shows....

Just because something is on a screen or in a drawing doesn't necessarily mean it will become a reality.

I have an engine that has a boiler with two larger flues for superheaters but there were no superheater elements. There are now because I added them.

[tsph6500]

the 3/8" OD flues will accomplish absolutely nothing in a model.

Now I have to break this news to my 5 little steam locos that have 3/8" flues that they can't run no more...

Seriously, they are 3/4" scale coal-burning locos BUT you can't say they don't work.

My 1-1/2" scale Mogul has 1/2" flues and is a wicked steamer, again on coal like the steam gods intended.

I would suggest that you go no smaller than 1/2" dia. flues on a 1-1/2" scale engine.

Then there's the question of what kind of coal you plan to burn, hard, soft or something in between. Hard coal works best on a large, shallow firebox because it needs lots of air. Softer coals burn much easier but produce more soot so you need the larger diameter flues like 3/4".

Locomotives are a system which needs the correct balance to work well.

[10 Wheeler Rob]

Jim,

Matt plans top build a large ground locomotive, and most ground track engineers are not happy with the flue cleaning schedule the smaller scale operators put up with. That is why people are recommending he build with larger flues.

Rob

[steam4ian]

G'day Matt

In my parlance flues are of larger diameter for superheaters to run through and tubes are the smaller diameter "flues".

Flue diameter is set by your superheater element size. Ideally the free cross section area 9allowing for the superheater element should be about the same as that for a tube.

Tube diameter is set by the length so that the cross section area to length ratio is between 50 and 80. Too large a diameter and you lose heating surface and the gas velocity is such you get laminar flow and even less heat transfer. Too small a diameter and there is too much resistance and pressure drop in the tubes and you need a harder working blast, more back pressure or poor steaming. Practical measures like cleaning also come into play so a coal burner might have tubes on the larger side whereas propane burners need a softer draft and smaller tubes will help this.

Regards
Ian

[Mike Walsh]

Jim,

Matt plans top build a large ground locomotive, and most ground track engineers are not happy with the flue cleaning schedule the smaller scale operators put up with. That is why people are recommending he build with larger flues.

Rob

Then they should run diesels

[David_T]

All those little 3/8 tube will equal about 1.7 sq inches of area. The 7/8" tubes equal about .5 sq inch area each. Four more of them would be a whole lots of less work to install. For reference the Railroad Supply Heavy Mike has a 12" boiler with 26 1" tubes.
That is 1/2 the inside diameter squared times pi for the area.
Regards cleaning, most persons clean from the smokebox end of the boiler, there is usually a number of items to block tube access located there.
Uncle put about 200 of those 3/8 tubes in his Newbie, but that was propane fired.
Research-research-research, then borrow someone else's design that has a good track record.