Coupling for 3" PVC to 4" Cast Iron

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SquishyBall

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Hi,
I keep finding hits to this site with so much great information so I'm going to register and post...

We have a 4" Cast Iron drain line. Need to cut it and connect 3" PVC. So I've been looking for the right coupling.

The Fernco 1056 series does not fit it. It says it connects PVC or CI, but our CI is slightly smaller.

The Fernco Proflex 3000-43 fits the 4" on the CI, and the 3" on the PVC, but it is not rated for underground.

What's the right fitting here?
Thank you!
 

wwhitney

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Both Fernco 1056-43 and 3000-43 have a spec of 4.46" on the 4" side. So if one fits the other should.

Maybe your 1056 was mislabeled? Otherwise I'm out of ideas.

Cheers, Wayne
 

SquishyBall

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So maybe this helps...

4" PVC is 14.2 around, which is 4.5 diameter. Great - it will fit that 4.46 spec on "Dimension A".
20221023_095628.jpg


3" PVC is 11.05 around, or 3.5 diameter. Great - it will fit the 3.52 spec on the "Dimension B"
20221023_095740.jpg


So that fitting would work great PVC 3 to PVC 4... but I'm going to CI...
My cast iron is smaller - see here?
20221023_095538.jpg


It is 13.55 around, or 4.3 diameter. 3/4" smaller in circumference than a 4" PVC. This 3/4" seems significant.

This 4.3 OD is too small for a 1056 - if I use that it will go on really loose. Or do I just put the 4" 1056 on there and start cinching it down? I don't want to cut it till I have the right part in hand to put on there cuz this is one of our main drains. :)
 

wwhitney

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Well, looking at Fernco's offerings, 1056-43 is the closest fit. I think cranking down from 4.46" to 4.3" won't be too extreme. But as I've not done it, perhaps someone who has will comment.

Cheers, Wayne
 
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