Thoughts on building a Yarrow?

[AlfJones]

Hello all.

I am looking at building up a Yarrow designed boiler. If you haven't seen one of these, then a simple GA is here:

http://www.modelengines4fun.com/postDetail/5/

However, I am planning to use only two sets of tubes, rather than three.

I have a few questions I was hoping someone could give me some thoughts about?

1) - Soldering the tubes to the lower water drums.
This will be a completely "blind" joint - I won't be able to see into the drum at all. I've not built like this before, and I'm not sure how I can make myself confident that all the joints are good. I won't be able to see penetration through the joints. This is going to be a fairly high pressure system, and while of course it will be hydro-tested first, I still want to be happy with the joints over time.

2) Again on the down comer tubes into the lower water drums - the design books I have show that the down-comers are flush with the drum. By this I mean that they do not project into the drum at all. I feel that it will make for a stronger joint if there is perhaps 2-3mm projection. It might make for a stronger joint, and will add a ( small ) element of baffling to what is going to be a very turbulent system.
Can anyone let me know if I might be making problems for myself by doing this?


3) All the design notes I have refer to the fact that I need to put baffles in the main water drum to control turbulence at the top of top of the tank in order to stop water pick-up with the steam collection, but not a single reference describes these baffles in any detail. Can anyone point me at any references to baffles boilers, or give me some thoughts?

Many thanks

Alf

 

[steamboatmodel]

Look in Model Boilers and Boilermaking by K.N. Harris page 165 & 166. He shows a nice design for a Yarrow. As he says though "A reliable means of supply a constant supply of feedwater is an absolute necessity, as the water content, relative to the evaporative capacity is very small.
Regards,
Gerald.

 

[Jasonb]

Model Engineer recently ran a very detailed series on building a Yarrow boiler, well worth reading. hink it was over about 10 issues.

J

 

[AlfJones]

Jason,

Do you know roughly when? I don't remember seeing it - I only get ME occasionally, it's MEW that I always buy.

It's not exactly a Yarrow, but very close indeed. Certainly easy to get to a true Yarrow design

 

[Jasonb]

Bit longer ago than I thought.

Started Vol 203, issue 4366, 17th Dec 2009.

J

 

[JorgensenSteam]

The boiler shown in the link you have posted has flat plates on the bottom drums, and I don't see anything that would act as a stay for these plates.
The tubes themself would not relieve the stress on the flat plates, and I believe they will flex and crack.

I think any design with flat plates and no stays is hazardous, so proceed at your own risk. The risk when a boiler fails, even a small boiler, is high, and it is not worth taking risks with unproven designs.

I think it is a big mistake to assume that because a boiler has been drawn up nicely, then it must be safe. I have heard of some serious accidents with people using flat unstayed plates on boilers and steam piping.

 

[Jasonb]

Pat surely the tubes will support the plate, it no different to the tubes in a throat/tube plate at the ends of a barrel. As the other end of the tubes are fitted to a curved surface they will have a job moving as to do so they would have to flex the side of the top drum

Whats of more consern is the unstayed end of the main drum as thats a far bigger flat area. Is there more detailed construction drawings as I can only see (we cant read online google books)

 

[steamer]

The thickness of the plate and the diameter have a bearing on the requirement for a stay on at drum end. There are calculations in the ASME code that can be performed to determine if additional reinforcement is required. If the ends are heavy enough, and the diameter is small enough, stays are NOT required.

There are no hard fast rules...every situation has to be evaluated individually.

Dave

 

[Maryak]

The thickness of the plate and the diameter have a bearing on the requirement for a stay on at drum end. There are calculations in the ASME code that can be performed to determine if additional reinforcement is required. If the ends are heavy enough, and the diameter is small enough, stays are NOT required.

There are no hard fast rules...every situation has to be evaluated individually.

Dave

All good advise................maybe if we knew the working pressure being aimed at then we might just get somewhere. I have seen this type of boiler operate between 200 and 450 psi at 12" : 1ft scale. I would hope in copper we are not aiming for more than 125psi.

 

[AlfJones]

Thanks for the comments all.

I have noticed that, in general, boilers have flat faced ends, which to me doesn't make a lot of sense. It would be far stronger ( although a more complex fabrication task ) to dish the ends, which would significantly reduce the requirement for staying.

I am looking to build a non-scale loco, so I also don't mind about changes to the innards as well.

 

[firebird]

Hi Alf

Sent you a pm.

Cheers

Rich

 

[mecanotrain]

Hello All,
I built a boiler Yarrow. See here:
https://picasaweb.google.com/109200417126637456771/ChaudiereYarrow#

VERY GOOD boiler Thm:

Best regards

 

[steamboatmodel]

Wow, that is one nice boiler. How well does it steam and what are you putting it in?
Regards,
Gerald.