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This topic has 12 replies, 7 voices, and was last updated 23 April 2021 at 16:55 by martin perman 1.

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22 April 2021 at 17:57 #541077
martin perman 1
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@martinperman1
Good afternoon gentlemen,

I'm currently having a culling session in my garage and have come across a simple steam oscillating engine as a kit of parts and also a piece of copper tube roughly 50 mm dia and i'm wondering if somebody can tell me if there is a minimum thickness for the tube thickness for making a simple boiler to produce 75 psi max.

Thank you,

Martin P

Edited By martin perman on 22/04/2021 17:57:54
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22 April 2021 at 17:57 #10807
martin perman 1
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@martinperman1
minimum thickness of boiler barrel
22 April 2021 at 18:02 #541079
Chris Gunn
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@chrisgunn36534
Martin, do you need 75PSI for a simple oscillator?

Chris Gunn
22 April 2021 at 18:10 #541080
Chris Gunn
Participant
@chrisgunn36534
Martin, just had a look at the Polly vertical, 1 3/4" OD copper is used, they do not give a thickness, the ends are 16 or 18G, so I would suggest the tube should be the same for a low pressure boiler, i have mad a few from 2" x 16G in the Polly style, as said 30psi will be plenty to run a smal engine.

Chris Gunn
22 April 2021 at 18:15 #541082
martin perman 1
Participant
@martinperman1
Gentlemen,

Thank you, I got the pressure from a book called Ellie the steam tram which uses an oscillating engine and the safety valve is set to blow at 75 psi so I used that as my starting point, I know mamod stuff runs on approx 30 psi.

Martin P
22 April 2021 at 19:15 #541098
Nick Clarke 3
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@nickclarke3
According to the magazines LBSC's Tich boiler is 18g with 16g tubeplates and 13g backhead
22 April 2021 at 20:44 #541112
nigel jones 5
Participant
@nigeljones5
75 psi is about 60 psi more than you will need, assuming its not doing much work. At high psi the steam pressure will cause the cylinder to lift off its pad thus defeating the point of using a high psi. I dont use 18g on any of our boilers as its not strong enough to use on an end plate which has a water sight gauge on it – the pressure will distort the plate and the gauge will break. 16g will do for your size of boiler. You could use 18g safely on the main tube but its so easily dented that its not worth it for us. Hope this helps.
22 April 2021 at 22:27 #541138
Simon Collier
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@simoncollier74340
The book mentions 75 psi because that is what the WeeBee safeties we buy from the US are set for. They are excellent. If you build the Ellie boiler with solid 3 mm end plates and the single central stay, you can't go wrong. The 2" tube I used in my G1 boilers is quite thin walled, maybe even 20 G. Interestingly, once my Ellie gets pressure up, as soon as it starts to run on the track, the gauge shows close to zero. It seems to use the steam as it is made. As has been stated above, a freely running oscillator needs very little pressure to run.
22 April 2021 at 22:28 #541139
martin perman 1
Participant
@martinperman1
The boiler design in the book has a 1/4" stay passing through both ends and the end plates are 2mm thick, it doesnt give the gauge of the tube though.

Martin P

Edited By martin perman on 22/04/2021 22:28:54
23 April 2021 at 10:54 #541212
Simon Collier
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@simoncollier74340
Page 34 in the Notes: 18 gauge or 1.2 mm.
23 April 2021 at 11:58 #541216
J Hancock
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@jhancock95746
Burst pressure of even the least spec 2 " copper pipe is well over 1000psi , the ends will come off well before

the pipe bursts.
23 April 2021 at 12:21 #541219
SillyOldDuffer
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@sillyoldduffer
Posted by J Hancock on 23/04/2021 11:58:02:

Burst pressure of even the least spec 2 " copper pipe is well over 1000psi , the ends will come off well before

the pipe bursts.

+1 This table at Engineering Toolbox gives working and burst pressures for various diameters and types of copper pipe.

Although the safe pressures reduce with increasing temperature, for 2" pipe it suggests:

Annealed working pressure 309psi.

Drawn Working 607psi

Annealed burst pressure 1910psi,

Drawn burst 3365psi

The working pressure of the weakest 2" copper pipe is 4 times greater than 75psi, and the same pipe has a safety factor of about 25. Drawn copper pipe can take twice the pressure. The pipe is unlikely to fail!

Dave

Edited By SillyOldDuffer on 23/04/2021 12:23:22
23 April 2021 at 16:55 #541249
martin perman 1
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@martinperman1
Gentlemen,

just picked up this thread after another session in my garage/workshop, thank you for your time, from what I read my piece of copper tube is adequate for the job.

Martin P
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