Steam dome seal

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Re: Steam dome seal

Post by NP317 » Mon Oct 23, 2017 10:37 am

FLSTEAM wrote:Another direction would be to cut the studding flange out then true it in the lathe again.
Re weld it back in place but this time be sure to tack it in place with lots more tack before the root pass.

John B
That sounds like way more work than setting up to correct the non-flat mating surface.
Messing with boiler welding would be my last choice, based on my skill levels.

And I would not expect to ever get a good seal on a surface with 0.010" gaps.
Take the time and effort to mill it flat, that's the best long-term solution. Worth the effort.
Just my thoughts.

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Re: Steam dome seal

Post by Greg_Lewis » Mon Oct 23, 2017 10:48 am

If all you are dealing with is a .010 gap, I'd explore sealing options. Ten thou just doesn't seem like that can't be solved with gaskets. In my Model A Ford days, I don't think we ever had a head-to-block seal that was even close to .010. I'd look for some FelPro gasket material at a good auto parts store. FelPro makes a variety of gasket materials and there are some that look like they'd be just right. I'd also try some Key Graphite Paste on the gasket. Another option would be a gasket from a piece of annealed copper sheet. Put thin gasket paper on both sides of that. I'd also spend some time on the McMaster site looking at their gasket materials . There's a lot more out there than just paper.
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Re: Steam dome seal

Post by Kimball McGinley » Mon Oct 23, 2017 12:36 pm

If I could not get it on the mill, I think I would mark, file, check, mark, etc. to get is as close as possible. Auto parts stores sell a product called Plastigage, used to check the oil film clearance between the crank and rod big end. It is a plastic string that is placed in the assembly, which is then tightened. When disassembled, the width of the smashed string corresponds inversely to the clearance it saw. This might be a great help, and they are very cheap. I think they come in various ranges.

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Re: Steam dome seal

Post by RET » Mon Oct 23, 2017 3:11 pm


I assume this is for 7 1/4"/7 1/2" gauge. If so, I would take the dome, chuck it in the lathe and cut a groove for an "O" ring inside the bolt circle. If this is for 1/8" scale, you could use a 1/4" thick "O" ring of the appropriate dia. to fit in the groove. For a 1/4" thick ring, leave it about 1/16" "proud" of the surface. This setup should have no difficulty in sealing the leak even if its more than .01"

I use "O" rings a lot to seal various things, fittings etc.

Richard Trounce>

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Re: Steam dome seal

Post by apm » Mon Oct 23, 2017 7:05 pm

I am reading through the replies and they all sound like way overkill. When I finished welding my steam dome it didn't look to nice. Like others getting the boiler mounted on the mill was a royal pain so I took the angle grinder cleaned it up as much as I could. Then I got a 1/8" thick Garlok gasket and some Permatex Indian head schellac at the local auto parts store and it doesn't leak.

0.010" would be wonderful compared with what I must have. The only minor issue is that with the permatex any time you break the joint plan on installing a new gasket. None the less they are cheap enough to get and for me was far better than figuring any way of getting the whole boiler onto the milling machine.

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Bill Shields
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Re: Steam dome seal

Post by Bill Shields » Mon Oct 23, 2017 8:19 pm

why don't you try a 1/16 thick, annealed copper gasket?

0.010" is nothing to take up (been there, done that....)

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Re: Steam dome seal

Post by Dick_Morris » Mon Oct 23, 2017 9:47 pm

why don't you try a 1/16 thick, annealed copper gasket?
The full-sized 1944 Consolidation we are rebuilding uses a ring of 5/16" copper wire, 26" in diameter. It's just inside of the dome cover studs. I can't tell from the drawing how the ends are connected, but silver solder would probably work. Operating pressure is 225 psi.

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Re: Steam dome seal

Post by BClemens » Tue Oct 24, 2017 5:53 am

There is always High Temp Silicone Gasket Maker from Permatex..... it's not high tech but it works - especially with such a small deviation in gap. But I personally would go with the annealed copper ring (McMaster Carr) or welded wire (home tig job) - maybe backed up with the HT silicone for resilience during heat transients. The copper would have to be squashed to its hardened state or re-torqued a time or two until it wouldn't expand with the heat and become loose when it cools down. We (at Jlab) use copper gaskets on 'knife edged' flanges on vacuum vessels (intergalactic vacuum (E-12))

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Re: Steam dome seal

Post by NP317 » Tue Oct 24, 2017 10:29 am

Previous two comments are useful.
To seal the steam dome lid on full sized steamers (180 - 200 psi operating pressure) we also (ref. Dick Morris) used 3/8" copper wire "H" shaped (actually a piece of trolly wire, because we had it available in quantity), silver brazed together at the ends. Initial tightening of the freshly annealed copper made an excellent gasket that sealed properly until the next year's maintenance cycle required removal of the lid. No re-torquing of bolts required.

But I'm pleased to read that "apm" seems to have resolved his issue with the steam dome seal.

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Re: Steam dome seal

Post by 10 Wheeler Rob » Fri Nov 03, 2017 2:14 pm

If the dome surface is flat. I would put use 1/32 or 1/16" flat commercial steam rated gasket with the gasket or rtv gasket compound on the non flat boiler surface only. This would allow dome removal since the gasket is glued just on one side.


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Chris Hollands
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Re: Steam dome seal

Post by Chris Hollands » Fri Nov 03, 2017 6:17 pm

Not sure what the top dome plate is , I machined o ring grooves in my dome covers , you could machine the groove slightly under full depth by 10 - 20 thou and that would give extra squeeze on the o ring and seal quite well with the pressure we run at , worked fine on my boiler at 300 psi test pressure .

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Re: Steam dome seal

Post by jlakes85 » Sat Nov 04, 2017 7:26 pm

I got a corrugated copper flange gasket installed and am now trying to get it properly seated. Is the objective to completely crush the ripples or is there something else?

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