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Old 01-12-17, 10:02 PM   #11
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Default Non-Tapered Threads

Daox,

I had a similar problem with a heat pump project.

Standard pipe thread is tapered and relies on a progressive interference fit to work.

There are other pipe thread systems that do not rely on tapered, progressive interference to work. Instead, they use a flat compression washer. The straight threads supply force to compress the washer.


If you were crossing systems, it would feel gritty, because very small bits of thread faces were being sheared off by your struggle to make it seal.

One give-away is that the thread shoulder (male and female) has a precision-machined surface.

There's a good chance that the damage to the threads is not completely fatal yet. If the machined surface of the shoulder is still intact and undamaged, you may be able be successful.

Of course, you need the proper straight-thread part and the proper compression washer.

If the damage has been too severe, there's epoxy.

Best,

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Old 01-13-17, 08:29 AM   #12
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Thanks for the tip AC Hacker. I'm aware of this. The unit we were working on had male NPT threads on the outside. They were definitely tapered.
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Old 01-13-17, 10:30 AM   #13
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When you said that "half the joints leaked", what are you referring to? Your heater only has two, IN an OUT, right?

Are they leaking?

Are half of all the joints you put together leaking?

This is very strange.

It sounds like you have been invaded by a different Physics that doesn't apply in the rest of the universe..

Maybe you should go copper at the heater, and switch to PEX ASAP.


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Old 01-13-17, 12:30 PM   #14
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Gasoila is used in the gas station business for installing underground tank fittings and more. You could likely find a petroleum equipment supplier (relatively) locally that would have it.

Hope this helps

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Old 01-13-17, 12:53 PM   #15
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We made a few other connections off the heater to ball valves for flushing the heater with vinegar.

In the end, we switched from the threaded fittings to compression fittings as that was another option that came with the heater. Those sealed up just fine.
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Old 01-13-17, 02:08 PM   #16
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To get 3/4npt fittings to properly seal it takes 100ft.lb, I have found that most npt fittings that leak are not any where near tight enough.
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Old 01-24-17, 02:58 PM   #17
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I use Loctite 55, its a cord with PTFE or the like on the cord, seems to keep on the thread better than PTFE tape and you can realy feel it's there when tightening up the joint.
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Old 02-06-17, 03:23 AM   #18
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Quote:
Originally Posted by stevehull View Post
Daox,

Don't feel bad . . . .

Teflon pipe tape works great if the threads are in good shape. More recently, the quality of metal pipe threading has gone to hell.

I never had leaks, in the past, but I get them regularly now if I just use teflon tape.

I still use teflon tape on the outside threads, but now always use pipe "dope" on the inside threads. A bit more time, but NO leaks.

Hope this helps.

Steve

ps pipe dope is messy and nasty . . .
+1 to this comment.
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Old 02-25-17, 10:09 AM   #19
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Quote:
Originally Posted by oil pan 4 View Post
To get 3/4npt fittings to properly seal it takes 100ft.lb, I have found that most npt fittings that leak are not any where near tight enough.
When I fitted propane into my camp I could not believe how hard I had to lock those fittings down. And that was with pipe goop. Basically it took every ounce of muscle I had and then going back the next day and doing it again.

Thx steve for the idea to wrap the inner threads and goop the outer. I will try that next time.

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