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Thread: Which coupling for 3" PVC to 4" Cast Iron

  1. #1
    DIY Junior Member takelargebites's Avatar
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    Default Which coupling for 3" PVC to 4" Cast Iron

    I need to connect my new 3" PVC drain line to the old 4" cast iron drain. The pipes are on the horizontal in the basement. Which Fernco coupling would be preferred? The 1056-43 Flexible coupling or the ProFlex 3000-43 ? It looks like either coupling would accomplish the same thing but it seams like the ProFlex would be more resistant to shear since it's banded.

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    Last edited by takelargebites; 12-15-2011 at 04:54 PM.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    You are correct, especially since the "Fernco" cannot be used for that application.
    Licensed residential and commercial plumber

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Above ground is when you need a shielded coupling; required by code.

    Plumbers always use shielded couplings.
    There are times in the ground, when you can use a non-shield coupling, since the ground is supporting.

    When you join pipes, it's important to measure the OD of the pipe.
    A new 4" cast iron pipe would be 4-3/8" OD
    An old 4" cast iron pipe can be as small as 4-1/8", which is considered a copper pipe size.
    If I have copper pipe size cast, then I use a mission copper coupling x no-hub. Which does work with PVC if it's standard waste sizing.

    Last edited by Terry; 11-07-2013 at 03:46 PM.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    quote; I generally only use banded ones myself, but thought they were only required underground.

    That is the ONLY place they are NOT required, but usually outside the building.
    Licensed residential and commercial plumber

  5. #5
    Illinois Licensed Plumber SewerRatz's Avatar
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    In Illinois shielded couplings are required underground. And above ground we are allowed to use no-hub couplings but must use a no-hub transition adapter on the PVC and or ABS pipe.
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  6. #6
    Moderator & Master Plumber hj's Avatar
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    When I was in Chicago, we never used PVC, ABS, OR No-Hub cast iron.
    Licensed residential and commercial plumber

  7. #7
    DIY Junior Member takelargebites's Avatar
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    My cast iron measures 4-1/4" OD. Does it sound like a Mission CP 43 (4" CI to 3" PL, ST, or XH CI ) would be the way to go? I'll see what the supply house has tomorrow morning and then track down an inspector to get his ok too.

  8. #8
    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by hj View Post
    When I was in Chicago, we never used PVC, ABS, OR No-Hub cast iron.
    I did not say Chicago, said Illinois. When I work in Chicago, we do not use PVC, ABS or no-hub. Still lead and oakem.

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