Combustion chamber boilers

[Deleted]

Good day all

A question on Boilers with combustion chambers, some of you will have seen my thread on LBSC's Heilan Lassie. She has a professionally built boiler that according to the drawings should have a combustion chamber. Being new to all this I have little idea what benifit this gives so put the question here. There does seem to be a chamber at the end of the tubes firebox side, I certainly can not see any tubes from the firebox. Although I haven't got the original cert for this boiler I do have the receipt that states it was tested to 180 psi and this is also stamped on the boiler itself along with some other figures which I do not know their meaning.

So guys are these type of boilers good? According to Curly who gives details for both types of boilers I get the impression the combustion type is better.

All comments welcome..

Pete

[alanstepney]

I feel they are more trouble than they are worth, in "our" sizes.

In addition, since Curly's day we have progressed in boiler design and can modify his (LBSC's) designs somewhat to improve their performance.
Comparing his designs using the work of Jim Ewins, for example, shows how good or bad, the boilers are.

[GeorgeRay]

Pete
The original LBSC design for Maisie was for a normal boiler he then produced a design for one with a combustion chamber. The concensus appears to be that the original boiler was a good steamer and soisthe Combustion chamber one. A combustion chamer boiler is more difficult to make and get steam tight. If anything goes wrong with the cross tubes in the combustion chamber however the chances of a repair are almost nill due to their position. However all the later full size locos had something akin to a combustion chamber but without the cross tubes, but in this case it was probably easier to fit and seal the necessary stays than in our case.

[jgb7573]

Whilst they might be more trouble than they're worth, particularly during building, if you've got one that your boiler inspector is happy with, I'd use it. No point in scrapping an otherwise good boiler.

[Deleted]

Thanks for the replies everyone...... George from what I can see there doesn't appear to be any cross tubes. The chamber has what I can only describe as supporting columns which are pretty large in diameter. There's two rows of them, not sure how deep they go, I can only see four of them which may be the total amount as the superheater tubes seem to be long enough for the remaining length of boiler. Hopefully I'll receive the drawings soon to see how the boilers made. The one thing that eases any concerns is how well the boiler seems to have been built, well that and the invoice stating the pressure tested. I need to make up some plugs to seal the various backhead fittings and also the dome before I can take it down the club for testing, I hope to do this over the next few weeks.

Kind regards

Pete

[redmog]

Tube Stays.

Pete.
I think it will have tube stays similar to the ones I have shown below.
They also aid water flow and increase steaming ability, theory has it!
I am building one the same when I can pull myself away from maintaining Simplex and making parts for the Gresley V4.
Chris.

Under side of combustion chamber before assembly.

[Deleted]

Thanks for the input Chris, thanks to your picture I now have a little more understanding about combustion chambers, for example I hadn't realised that the columns allowed water in, makes more sense now. You can see the columns in my picture, I strained to see into the chamber and there are at least another two columns in the chamber, I can't tell if there's anymore due to my head being to big, now where have I heard that before...

Cheers

Pete

Attachments:

[redmog]

Six Tube Stays.

You've got it!
They look like this from above.
That's why comments have been made about their inaccessibility once affixed within the outer wrapper.
I wish I could find a way of testing mine before I 'stick' them together.
I'm open to advice from anyone who has been down this path.
Chris.

[GeorgeRay]

Chris
The only way that I know of is to blank off the grate with a thick plate and rubber gasket clamped externally over the top of the firebox and also the fire door opening, then pressurise the firebox any leaks around the cross tubes will soon show up. This can be done with Maisie because the fire box bottom is straight, not sure about Heilan Lassie though, isn't there a change in angle.

[Shawki Shlemon]

Combustion chamber increases the heating surface , hence steam making , most Pacific's had this type of boilers . When I built the NSW C38 in 5" G , it had combustion chamber after talking to others I came to conclusion that we really don't need it so I left it out and the engine didn't suffer in performance , admittedly it has not been checked against another with combustion chamber .
In our club one person I know very well , he had a C38 in 3.5" G and built the boiler with combustion chamber , on the test day he discovered there was a leak in one of these tubes , he is a person very careful with his money , the boiler inspector in the club at that time allowed him to repair by cutting a window in the barrel adjacent to the leak , fix the leak and then repair the barrel .This was done successfully and the engine ran for many years after that , he has moved on to 5" g engines and I haven't seen the engine for a long time but I know he still have it .
Repair may be difficult but not impossible .

[steam4ian]

G'day Pete

The usefulness of the combustion chamber will probably depend on what type of coal is being burned.

If the coal is low on volatiles, e.g. anthracite or char, then the flame length is short so that combustion is complete before the gases get to the tube plate. If the coal has more volatiles there will be a longer flame length and you need the additional flame path provided by the combustion chamber before the hot gases enter the tubes. Combustion is quenched in the tubes.

Regards
Ian