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Sealing boiler fittings

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Martin Cottrell14/08/2011 16:54:14
297 forum posts
18 photos
Hi all,
 
I have recently finished building a small vertical boiler and I'm having problems stopping the steam fittings from weeping under pressure. The pressure test was fine because I used blanking plugs in the fitting flanges, wanged up tight with a fibre washer under the heads.
 
Obviously the fittings need to be tightened down to a point where they seat in a particular alignment, most importantly the 2 halves of the water sight glass. Although I have used fibre washers under these fittings, varying the thicknesses to get correct alignment when tight, I am still getting seeping under pressure from about 10-15 psi upwards. The fittings are all 1/4" x 40 tpi. I would like to know does anyone use a liquid retainer such as studlock in these situations to seal the threads or would I be better using something like PTFE tape?
 
Advise would be much appreciated!
 
Regards, Martin.
JasonB14/08/2011 16:57:16
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25215 forum posts
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You can buy soft copper washers that come in varying thicknesses, these should give you the adjustment you need to get things lined up. Most ME suppliers will have them such as Bruce, EKP, etc.
 
Best to avoid PTFE tape as small bits can get under the seatings of clacks and safety valves. Studlock will be too strong but you can buy liquid PTFE but I would stay with the copper washers
John Baguley14/08/2011 18:16:51
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517 forum posts
57 photos
I use Loctite 242 threadlock. Wouldn't use anything else now. You may need some washers to get the fittings in the right alignment when they are tightened up.
 
John
Windy14/08/2011 18:52:49
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910 forum posts
197 photos
On my flash steam boiler stainless steel pump valves they are sealed with locktite and hydraulic tested to 3500psi with no leaks.
 
Windy
Martin Cottrell16/08/2011 11:50:15
297 forum posts
18 photos
Thanks for the replies Jason, John & Windy! I think I'll go for both of the options suggested and use copper washers with a few drops of Loctite for good measure. That's 2 more items to add to my shopping list for the Bristol ME exhibition this coming weekend!
 
Regards, Martin
DMB16/08/2011 13:50:00
1585 forum posts
1 photos
You could also use Green Hermetite as a gooey sealer - it never sets so easy to unscrew fittings. Do Not use Red version - it sets solid and hard.
 
John.
Ian S C16/08/2011 14:19:53
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7468 forum posts
230 photos
I use Loctite 567 Master Pipe Sealant, it has a temperature range o -55*C to260*C. It does not lock the thread, so you can undo it easily, it's proberbly the same as what Windy uses. you could use 569 Hydraulic Sealant. Ian S C
Oldpeter23/10/2011 10:20:35
5 forum posts
On taking my second hand boiler fittings off, I discovered aluminium washers were used, corroding the threads to blazes - will have to replace the fittings with larger ones, Drlling it out and re-tap, but I am not sure in what threads (standard and tpi) the fittings are available - Any suggestions. I have an old Stuart Turner 504 boiler. Also very difficult
(? impossible) to find the correct size water gauge or do I have to use one with one free floating end?
Ian S C24/10/2011 10:29:48
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7468 forum posts
230 photos
If you need washers, use annealed copper washers, you can make your own. reanneal when replacing them, after taking the fitting out and putting it back.
Aluminium will help prevent corrosion on a asteel boiler, working as a sacrificial annode, zinc is even better.
On the cooling system of one of my hot air engines I ended up with a copper hopper for the water, and decided to use some aluminium fins imersed in the water, and exposed to the air for extra cooling. One day I , for some unknown reason, put the volt meter on the aluminium and the copper, result .5 volt, nothing much as current goes. Ian S C

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