Which coupling for 3" PVC to 4" Cast Iron

Takelargebites · Dec 15, 2011

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.

hj · Dec 15, 2011

You are correct, especially since the "Fernco" cannot be used for that application.

Sponsor · 2022-01-29T12:20:58-0800

Terry · Dec 16, 2011

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.

hj · Dec 17, 2011

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.

SewerRatz · Dec 17, 2011

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.

hj · Dec 18, 2011

When I was in Chicago, we never used PVC, ABS, OR No-Hub cast iron.

Takelargebites · Dec 18, 2011

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.

SewerRatz · Dec 19, 2011

hj said:
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.

LesP · Sep 22, 2018

Terry said:
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.

This is great information, Terry -- thank you. My "vintage" cast iron drain has an O.D. of 4.25" and I'm connecting it to 3" ABS.

Would a Fernco 3000-43 be able to ratchet down tight enough? The 4" side of the coupling has an I.D. of 4.42".
Alternatively, I could get a 3006-43 made for copper, but would the 4.13" I.D. stretch enough to get it on the pipe without a massive fight.

Feeling like Goldilocks here...!

Terry · Sep 22, 2018

The main thing is to have the rubber bushing under the sleeve close enough in sizing to allow the bands that tighten it to remain straight.
They do make many different sized in couplings now to make the correct transition between the different pipe sizing. It does need the metal wrap to prevent shifting, which can get pretty ugly over time.

Jadnashua · Sep 22, 2018

NOte, if you can have access to a hub, you can use a rubber donut to make the transition. While PVC is standard, the ID of a hub is not, so they make lots of different donuts to fit. You may need some dishwasher detergent as a lubricant to slide the pvc and donut in place. It's sort of like Goldy Locks...it needs to be just right, so that's why they make multiple sizes of donuts to fit various hubs. Too tight, and you won't be able to insert it...too loose, and it will leak. Done right, it works fine.

Which coupling for 3" PVC to 4" Cast Iron

Takelargebites

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hj

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