Boiler Design – issue 4765

[Andy StopfordParticipant @andystopford50521]

The Haining designs are useful as an approximate reference, but you can get copies of the original works drawings from The Museum of English Rural Life and rescale and adapt them to your own requirements. They’re not cheap if you need a load of them, but better value to my mind then buying the Haining ones.

I’m working on a 1/12 scale Z7S, a scale which is somewhat…challenging for such a complicated machine, but its as big as my lathe and indoor workshop allow, and getting the MERL drawings is much better than re-scaling something that’s already been scaled and changed to suit the facilities of the 1980s.

At this moment my 3d printer is making a mock-up of the coiling gear – I was quite unable to translate Haining’s design into anything workable and I don’t have a works drawing for that (there isn’t a full set for the Z7S) – 21st century technology to the rescue here for something that would be very tiresome to iterate multiple test pieces using old-school methods.

I’ll probably use the printer to make patterns for some cast bits too(not strictly necessary to use castings for a model of this size, but I have a little propane fired furnace, so why not give it a go – my limited experiments so far have come out far better than some of the commercial Minnie ones I foolishly bought).

[Bob Worsley]

On Bob Worsley Said:

Just dug out the emails when boiler kit bought, and contacted Neil Tyler about the changes and never got a reply. Reeves saying it is up to the designer, they just supply what is asked for, Neil Tyler says it is due to the supplier of the kit. So I ended up with £670 worth of scrap copper.

 

If you buy anything mail order you can return it for a full refund no questions asked. Thats UK law. There might be a time limit, not sure, ask citizens advice

[JasonBModerator @jasonb]

I have made contact with Alan Brown, one of the authors and invited him to comment. He is a forum member.

[duncan webster 1]

On duncan webster 1 Said:

On Bob Worsley Said:

Just dug out the emails when boiler kit bought, and contacted Neil Tyler about the changes and never got a reply. Reeves saying it is up to the designer, they just supply what is asked for, Neil Tyler says it is due to the supplier of the kit. So I ended up with £670 worth of scrap copper.

 

If you buy anything mail order you can return it for a full refund no questions asked. Thats UK law. There might be a time limit, not sure, ask citizens advice

That limit is normally 14 working days after delivery, so this case seems time-expired.

[duncan webster 1Participant @duncanwebster1]

What diameter and pressure is the BB boiler? The Aus code allows 90 psi for a 5″ diameter 2.5 thick shell. Sorry for the mixed units, peopld of my antiquity had to cope with both

[JasonBModerator @jasonb]

5″ OD x 75psi.

Though I would want to make an allowance for the fact it is a ploughing engine so quite long and unsupported plus that big winding drum slung below will put loads into the barrel if you pull anything. There are no stiffening pads for the drum bracket, though there are for the cylinder and valve bracket

I assume that the original 13swg design was found to be a bit wanting and that is why Haining upped it to 10swg (0.126″)

[Andy StopfordParticipant @andystopford50521]

Doesn’t Haining also suggest using a steel shell round the boiler to take the loads from the drum and front axle?

[JasonBModerator @jasonb]

He does give it as an option in the article but the photos in the article are of a boiler with the brackets soldered direct to the barrel and that is also what is shown on the drawings. Even if you did make it I don’t think you could slide it past the clack valve bushes or fit the smokebox which is still shown to fit the end of the boiler not the steel tube so boiler taking the axle loads

[duncan webster 1Participant @duncanwebster1]

There is a separate table for traction engines where the boiler is subject to external loads, thats the figure I quoted. I wouldn’t have thought you’d be doing a lot of ploughing with a 2″ scale model

[JasonBModerator @jasonb]

Yes but with a ploughing engine typically having a boiler barrel 50% longer than a traction engine I’d want to see some additional thickness even over the thicker TE table.

You have not see Harry Williams pulling loads accross a field with his pair of Kitshons or Ross Bishop running his 3″ under load. generally the models are run with a load rather than an actual plough as rally organizers are not keen to have the grass torn up and it is also hard to find someone smallenough to sit on a 2″ scale balance plough to steer it

https://youtu.be/hAcpujv-_4g?si=t8j70PygSsoB_OD2

[JasonB]

On JasonB Said:

Thank you JasonB for pointing out an error under Example 2, a boiler by KN Harris. The figure 3 in the YPM formula should indeed be 2.

This results in a calculated YPM thickness of 0.112″ (Not 0.122″ as you stated) resulting in the Harris thickness being 77% of YPM not 55% as in the Article.

I do apologise to MEW and our readers for my mistake.

Please note that this in no way detracts from the philosophy nor the conclusions of the article.

A revised section of the calculation referred to is shown below.

 

[MEinThailandParticipant @meinthailand]

Thank you JasonB for pointing out an error under Example 2, a boiler by KN Harris. The figure 3 in the YPM formula should indeed be 2.

This results in a calculated YPM thickness of 0.112″ (Not 0.122″ as you stated) resulting in the Harris thickness being 77% of YPM not 55% as in the Article.

I do apologise to MEW and our readers for my mistake.

Please note that this in no way detracts from the philosophy nor the conclusions of the article.

A revised section of the calculation referred to is shown below.

 

 

[JasonBModerator @jasonb]

Thanks for that and also correcting my Typo, just looked at what I wrote when working it out and it was 0.112.

 

That was based on your 6″ but for the Harris example his 6″ is the Inside diameter in which case 6.173″ should have been used in the calculations, this gives 0.115″. However as this has a similar effect on both methods the percentages stay about the same. (Assuming Evans is using OD as I don’t have his book)

I’m sure those that have posted hera are keen to know why we have not seen boiler failures using the old methods and will therefore need convincing of the need to change the way things are done particularly as you say your results consistantly give a thicker boiler shell which will add to the already hight cost of a copper boiler and the resulting thicker barrel will have a knock on effect on room to get tubes in, reduced water space and reduced grate area. What are your thoughts on this and assuming the flat plates are also annealed what do you propose to calculate their thickness and subsequent stay spacing?

[Charles LamontParticipant @charleslamont71117]

Erm … The pressure is exerted on the inside of the boiler shell.

[Michael GilliganParticipant @michaelgilligan61133]

Yea-But the failure will start on the outside skin, which is in tension

[ just a thought from one uninitiated in the art, but observing from afar ]

Please shoot me down if that’s nonsense.

MichaelG.

[JasonBModerator @jasonb]

Charles, I was making the point that the suggested YP method as in the article used D as the OUTSIDE diameter so should have been altered for the calculation. If however the ID should have been used then that is not what is shown so could that be another error?

[JasonBModerator @jasonb]

Online calculator also used OD of tube.

Interesting if you put the OD of harris’s boiler in and fiddle with the thickness until you get 180 (2 x WP) the number that works is 2.35mm. Now to me that is not far off the 3/32″ that Harris says “will be perfectly satisfactory”  Though the online calculator does not allow for a butt strap.

[JasonB]

On JasonB Said:

5″ OD x 75psi.

 

I assume that the original 13swg design was found to be a bit wanting and that is why Haining upped it to 10swg (0.126″)

I now wonder if the reduced thickness came about from either UK tube stocks or simply the shortage of copper back then. BT switched to aluminium busbars and we could not get some cable at all.

[MEinThailandParticipant @meinthailand]

JasonB, since we prepared the Yield Point Method proposal over 6 months ago we have been busy researching and refining the subject almost on a daily basis including flat plate analysis and FEA modelling.

We have also compared the commonly adopted ‘standards’; UTS method, YPM method and the Australian Code by AMBSC.

We have reached a conclusion that should help to resolve misunderstandings of the differences between these methods and provide clarity for the design of copper boilers going forward.

We will be able publish these conclusions when the model engineering community is a listening mode rather than a criticising mode. I don’t feel that we are that point yet, which is shame because our intention is always to help the model engineer with our research and do I think we have a lot of value to offer.

 

 

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