Advice about boiler for 2″ Minnie

[PackmuleParticipant @packmule]

Getting confused by different advice re the thickness of the boiler. If I just double up its 5mm but I've seen on different forums that 3mm is fine for the 2".

Can anyone give me a diffinative answer ?

I don't want to waste money buying 5mm when 3mm is ok but at the same time i don't want the reverse where i buy 3mm and its not good enough for the job.

Any boiler inspectors etc care to comment?

Thanks,Bob

[PackmuleParticipant @packmule]

[Nigel BennettParticipant @nigelbennett69913]

3mm might well be OK as far as resisting internal pressure is concerned. What you have in a traction engine boiler is a structural component, and I've often seen miniature locomotives pull a bit of a wheelie and then thump back down on to their front wheels when working hard with massive loads. Not a good thing to be doing if you've only got 3mm of soft copper tube. I'd go for the 5mm and hang the expense.

[JasonBModerator @jasonb]

I can't really see what you are doubling up to get 5mm.

The Barrel is 16swg on the 1" so use 5" x 10swg on the 2" which is 3.25mm thick and I have seen several built with that size tube.

Most of the other plates are 16swg on the 1" so nearest metric would be 3mm

Tube plate and backhead are 13swg so that is the only one where 5mm would be the nearest available

5mm for all of it is not just a big increase in cost you will also loose grate area and its hard enough to keep a fire going in teh smaller engines without reducing the size of the fire. Also if using 4 or 5mm material you will have to go for a rolled barrel as that thickness is not available off the shelf in tube form. My almost identically sized Fowler is 10swg barrel and 3mm sheet so no need for thicker though I would go for more tubes 11/16 to 1/2" dia rather than doubling up the 3/8" to 3/4"

Edited By JasonB on 23/07/2013 13:12:21

[nigel jones 5Participant @nigeljones5]

10swg is plenty strong enough for what you require (avoid wheelies!!). Even at this spec you will need a lot of heat to get it to flow!

[PackmuleParticipant @packmule]

Jason ,

sorry my mistake ,I don't know where I got 5mm from either

I was thinking of using 18 3/8 tubes. or will they clog too easily ?

Cheers,Bob

[JasonBModerator @jasonb]

Given that you will have a 5" dia boiler its worth looking at the other models with a similar size and what they use in the way of tubes.

2" BB1 5" barrel has 14No 1/2" x 20swg tubes

2" D&NY 5" Barrel has 13No 1/2" x 20swg tubes

2" K5 (16nhp) 5.75" barrel 13No 1/2" x 20 and 3No 5/8 x 20swg tube

2" A7 4.75" barrel 21No 7/16" x 22swg tubes

So I think I would be inclined to go with 13-14No 1/2" tubes. But as I have said before run it all past your boiler inspector before buying any materials.

J

[nigel jones 5Participant @nigeljones5]

remember that your boiler inspector will be interpreting the green book rules…if he has a low iq you may be in for a battle!

[Author]

Posts