Cast to ABS Coupling - shield buckling

Discussion in 'General Plumbing Help' started by jmterail, Jan 7, 2019.

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  1. Jan 7, 2019 #1

    jmterail

    jmterail

    jmterail

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    I'm doing an ABS to cast transition.

    4" cast connected to a 4" to 3" ABS bushing.

    The bushing has a spigot end that should be identical diameter to 4" ABS pipe, so I figured a regular hubless 4" shielded coupling would work. (I used this one: https://www.americanvalve.com/product/rnhhd/)

    Problem is, the diameter of the cast seems to be slightly off - it's a slightly larger diameter than the ABS, to when tightened, the coupling shield buckles (since the ABS-side clamp has to be tightened more than the cast-side clamp).

    I poured some water down and it doesn't seem to leak - but it doesn't look to pretty (pic below).

    Is there a better coupling for this?

    Also wondering if I can wrap the ABS with a bit of sealing tape to increase the diameter to better match the cast?

    Image-1 (3).jpg
     
  2. Jan 7, 2019 #2

    voletl

    voletl

    voletl

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    That is a tubular by pipe transition coupling. You need a diffrent coupling.
     
  3. Jan 7, 2019 #3

    jmterail

    jmterail

    jmterail

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    Gaa, you are right.

    That was all the big-box stocked.

    Looks like ideally I would go for a fitting specifically designed for cast to plastic - https://www.fernco.ca/sites/default/files/dimensional-drawings/pdf/3000-44.pdf

    No idea where I could buy one though.

    Home Depot also stocks this one:

    https://www.homedepot.ca/en/home/p.no-hub-coupling-4.1000117478.html

    Says it will connect plastic/cast iron - but something tells me it's going to be the same issue as with the last one - where the fitting is not designed to accommodate pipes of slightly different sizing.
     
  4. Jan 7, 2019 #4

    Geofd

    Geofd

    Geofd

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    the older cast iron has 2 different markings (sv service weight) (xh extra heavy) they both are larger abs/pvc you can find these couplings at a plumbing supply house
     

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