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3/4" copper steam exhaust

Bending Copper Pipe

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John Nic26/03/2020 20:32:01
3 forum posts

I am building a 5" Gresley V2 and each of the three cylinders has a 3/4" diameter exhaust pipe that, scaling off the drawing, has 1.5" radius bends before joining together below the blast pipe. Is it possible to bend such pipes with this radius or am I going to have to find a way of fabricating the whole thing. Also would 18g or 20g be right. There is no information on the drawings.

John Nic05/04/2020 22:31:49
3 forum posts

I am wondering whether swept right angled plumbing fittings might be suitable/adaptable for this rather than trying to bend the pipes. Has anyone used these before?

Its a Michael Breeze design. I have looked at the Martin Evans V2 drawings in this area and these just use right angle elbows and much smaller bore. Seems a bit harsh to me, not exactly a smooth flow.

Nigel Graham 206/04/2020 00:27:41
589 forum posts

I'd have thought the swept bends the right approach. The full-size parts might well have been castings so able to take a relatively sharper curve that could have been managed with its own equivalent, bent steel pipe.

Right-angle elbows would certainly give a turbulent flow and hence some resistance, but whether it would have any significant effect in this application I could not say.

Does seem a large diameter though. I wonder if that is a scaling result more than design need: a cast exhaust branch would have been quite thick-walled.

 

[Edited to correct a missing word!]

Edited By Nigel Graham 2 on 06/04/2020 00:28:38

Dave Wootton06/04/2020 06:18:23
59 forum posts
8 photos

If it's any help there are a range of copper swept bends, elbows and tee's available in imperial sizes for refrigeration pipework, from 1/4" in steps of 1/8". These are stocked by most refrigeration suppliers, HRP, Dean and Wood are amongst the suppliers with national branches, and in normal times can be picked up from their trade counters ( they do cash sales without an account), alternatively I recently bought some from Ebay , there were suppliers with a good range on there, which could help in these strange days.

Lend themselves very well to fabrication of complex manifolds, two swept bends can be cut and shut to make a very nice exhaust tee, and have solved smokebox plumbing problems in the past.

Refrigeration machines use pressures far above anything we would use for steam, unless it's all gone horribly wrong!

Dave

Edited By Dave Wootton on 06/04/2020 06:18:48

Edited By Dave Wootton on 06/04/2020 06:21:44

JasonB06/04/2020 06:56:07
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17882 forum posts
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I have used "full crossover" fittings to get a tight bend. Cut off the endfeed sockets & 45deg part and make a thin ring to slip inside the joint so it is not just a simple butt joint and silver solder. Really tight bends can be cut from solid with ball nose cutters and then fettled externally to look right if visible.

John Nic06/04/2020 08:09:59
3 forum posts

Thank you for this information. I am going to try the cut and shut route. Because it’s the centre cylinder it won’t be visible inside the smoke box saddle. If the diameter is too large will this affect performance?

Ady106/04/2020 09:08:33
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3649 forum posts
514 photos

cz pipe bender?

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