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Steam Stationary Engines, Traction Engines

Worn try-cock threads. Help needed


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  #1  
Old 04-05-2007, 01:12:01 AM
tirediron tirediron is offline
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Default Worn try-cock threads. Help needed

Okay... I've got a wee problem with the try cocks on our club's Sawyer. At some point, replacements were put in with so much force that the threads are pretty much stretched. The cocks hold, but I'm not happy, they're turned right up to the last thread, and even at 85 lbs, you can see wisps of steam.

What can I do? Drilling and tapping isn't an option unless I remove the cross-shaft, and even then because of the longitudal stays, it's going to be difficult to get get a drill on the backhead.

Welding and rethreading is not a good choice for the same reason and because our boiler inspector has a kitten every time I use the words 'weld' and 'boiler in the same sentence.

What I had thought to do was make a set of adapators out of solid stock with a longer than normal taper, so that they would turn up tight even in the stretched threads.

Does anyone out there have other suggestions? Experience with this?
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Old 04-05-2007, 02:43:13 AM
F12Mahon F12Mahon is offline
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Default Re: Worn try-cock threads. Help needed

Can you use some pipe dope?

If you make an adapter it won't need longer threads...just fatter threads. Tapered pipe threads are tapered 1 inch in 16 inches. If you want your fitting to be in 1/4 inch less than a normall fitting your calculations would be as follows. .25/16 = x = diameter in inches the fitting needs to be larger. .25/16 = .015625 inches. You might be able to use adjustable dies to make it bigger. If they aren't available single point threading on a lathe would be the way to go.

If you make adapters is there enough room for them?

Eugene
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Old 04-05-2007, 08:31:54 AM
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AndyG AndyG is offline
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Default Re: Worn try-cock threads. Help needed

What thread size are your trycocks? 3/4" NPT probably. I think that you are on the right track. Make a custon 3/4 to 1/2" bushing that will seal in the existing threads. You will have to get some 1/2" NPT trycocks though. I would not recommend that you try to make a bushing that will still accept the 3/4" trycocks because the wall thickness will be to thin and it will crack.
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Old 04-05-2007, 09:10:10 AM
Pete LaBelle Pete LaBelle is offline
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Default Re: Worn try-cock threads. Help needed

Make sure to chase the threads with a tap prior to putting in your "fix".
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Old 04-05-2007, 04:53:13 PM
Mark L. Jordan Mark L. Jordan is offline
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Default Re: Worn try-cock threads. Help needed

Quote:
Welding and rethreading is not a good choice for the same reason and because our boiler inspector has a kitten every time I use the words 'weld' and 'boiler in the same sentence.
Keep saying them in the same sentence. Maybe your boiler inspector will eventually learn something.

MJ
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Old 04-06-2007, 02:17:12 PM
Allen
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Default Re: Worn try-cock threads. Help needed

Quote:
Originally Posted by tirediron View Post
our boiler inspector has a kitten every time I use the words 'weld' and 'boiler in the same sentence.
Don't need any furry type kittens, but if you can manage to get him to have a Kitten..... say about 16HP....then you can always send it to me. They are just odd enough looking to be cute.
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Old 04-07-2007, 02:31:55 PM
tirediron tirediron is offline
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Default Re: Worn try-cock threads. Help needed

Thanks for the input everyone; I think the custom bushing is the way to go. I've doped up the threads but it's still not secure enough for my liking. When I said "Longer" threads, what I meant was a longer taper, that is, continue the taper out so that there were more threads of a larger diameter than normal on a 3/4 tapered fitting.

(As for the BI & the welding... new guy, and while he can tell you everything there is to know about an espresso machine, he's a little weak when it comes to 'real' steam!)
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