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Thread: CVPC Transitions & General Threading Question

  1. #1

    Default CVPC Transitions & General Threading Question

    Questions for some pros:

    1) On the copper to CVPC transition adapters that are out there, am I good to go simply using the "better" hot water system trans unions on both cold and hot water supply lines (vs the cheaper crap you can supposedly use for just cold water lines)? I'm going 3/4 copper to 1/2 CVPC for two new 15 foot runs through floor joists, so wanted some flexibility of material... other wise I'd have the torch out hands down.

    2) I'm hearing that male threaded copper to CVPC transitions should be avoided all together. True? Any type/brand of transition that some pros like to work with? I want to make the least risky (and code compliant) transition, as my only future access will be through my living room ceiling.

    3) General: Are the MIP and FIP threads on these copper to CVPC adapters the same as what I would call NPSM (National Pipe Straight Machine)? I wasn't sure if these were the same things, and/or if the transitions were tapered for the copper adaptation side of the fitting? What I did find... is that I have a shower valve with a 1/2 inch NPSM fitting on it's output port, and the 1/2 CVPC X 1/2 brass FIP transition thread does not seem to be a good machined fit - like it catches two threads and stops cold. I feel like something is up.

    Hope my novice babble makes some sense.

    Rick

  2. #2
    Plumber Cass's Avatar
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    For the amount of flex you get over 15' copper should be fine but you can use CPVC. When connecting the 2 you can trans with a CPVC male adp. into a copper female adp. not the other way around or use the adp. that are made specificly for that purpose.

    If your only catching 2 threads something is up. NPSM and IPT must not be the same.

  3. #3
    Plumber jimbo's Avatar
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    Threaded fittings like male and female adapters are TAPERED pipe threads. Straight threads are different, and are not used where the threads are the sealing point. Doesn't work. Straight thread are used for mechanical joints, where it is mandatory to have full thread run. The only place you commonly find straight threads in household plumbing is the shanks on a lav or kitchen faucet. This is so the hold-down nut can be run up tight. Whatever connector is used to attach the water line also has straight threads and the seal is made by some kind of cone washer or flat gasket. The 7/8" ballcock connector is also straight, and is sealed by gasket.

    What brand of shower valve do you have with straight threads on the water inlet connections? This would be unusual.

    As to your other points, PVC is not allowed inside the dwelling, even on the cold side. CPVC is ok when allowed by local codes. As mentioned, plastic female adapters should never be used in transition to metal. Use male plastic, female metal.

  4. #4
    In the Trades Bob NH's Avatar
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    " NPSM threads are actually parallel but have the same pitch as NPT/NPTF. These threads are typically used inside swivel nuts for holding only. Contact between the 30 internal chamfer of the male pipe thread and the seat inside the swivel provides the seal."

    http://www.machinedesign.com/ASP/str...tedArticle.asp

    You have a wierd shower valve that should have probably come with mating fittings.

    From your description, I gather that you have a valve with a male NPSM thread since you refer to trying to mate it with an FIP adapter. There is an example of a mating part in a Table at the link.

    You should go to the supplier and find out what fittings are available for the valve. You might need to go to a supplier of hydraulic equipment. Such fittings are often steel because of the high pressures involved.

    You might check whether the fitting has an internal diameter that will accept a copper tube soldered directly into the valve. I have seen valves with a male thread that will accept standard 1/2" copper pipe. I replaced one such last week.

  5. #5

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    Jimbo-

    Don't you post over on John's tile forum also? Or is that a differnet jimbo

    No PVC... just CPVC!

    The shower valve is Danze, and it isn't the inlets, but the output that is configured with a 1/2 NPSM male head (according to thier docs). The inlets are indeed 1/2 NPT tapered threads which makes sense to me too, since they adapt to normal copper fitting. My understanding is that NPSM stands for National Plumbing Straight Machine... me guessing that this is truly means it is a straight thread. BUT WHY?? Is there a way to see the tapering? All I can figure is I'll bring this thing over to a Home Depot and start playing around

    I figured all of those copper to cpvc fittings are tapered too, and that seems to back up the fact I indeed have "straight" threads on this mixing valve output. OR... the transition I have is simply defective with bad threading. Time will tell.

    Cass might have hit the nail on the head... with 15 feet I can probably get enough bend and wiggle out of the 1/2 copper to make the run without using this CPVC crap, but I hated the prospect of too many coupling welds every few feet No offense to the CPVC fans!

    Peace!

    Rick

  6. #6

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    Bob NH-

    Thanks for that... at first I thought you were quoting your own knowledge when you got started! I was in awe

    Hmm... this sounds a lot like the type of parallel thread one would encounter on a compression fitting with a flare on the pipe right? Only trick here is that the output male end on the valve has no cone. Fricking euro crap! Since the output will feed a diverter valve above it, I wonder if they make a pre-made "merger pipe" to couple them together? I'll check the diverter and see if it has emplyed the same faulty engineering wisdom.

    Rick

  7. #7
    In the Trades Bob NH's Avatar
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    The external male thread may have an INTERNAL cone to match a mating part. Per the link: "Contact between the 30 internal chamfer of the male pipe thread and the seat inside the swivel provides the seal."

    You might find that a 1/2" pipe size ball cock adapter with gasket will fit it. If you can find one that accepts 1/2" copper you could fit that to the next part.

  8. #8
    Plumber Cass's Avatar
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    Why don't you get a roll of soft copper and pull it through with no couplings other than at each end?

  9. #9

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    Cass-

    I'd be OK with soft copper vs "hard" pipe with less bendability for water runs to a tub? And I can get 1/2 inch soft copper (same stuff as one would use on AC freon runs right)?

    That would be great if such a thing is acceptable... which is why these forums are so great.

    Thanks for the advice/support!

    Rick

  10. #10
    Plumber jimbo's Avatar
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    SlickRick: I visit JohnBridge, but only for enlightenment; I haven't posted there. I post on other plumbing and electrical forums, but not as Jimbo.....that name seems to get "taken" earyl in a forum lifecycle!

  11. #11

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    Just to get some clarifications... it seems the "best" method for making a copper to CPVC transition is to use the slip fitting unions that solder brass to copper directly on one side? I'd like to avoid any threaded connections on the metal to metal side of the equation. Is this smart?

    Rick

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