Fernco fitting question

[drew53813]

My plan will be to join ABS to cast iron. Do you want the new ABS to but right up against the cast iron or can you allow for any size gap between the cast and ABS before securing the fernco fitting? Thanks

 

[Reach4]

See if www.terrylove.com/forums/index.php?threads/fernco-donut-tight-ness-question-maybe-too-loose.56196 helps.

 

[Sponsor]

 

[Smooky]

You want it to be a smooth transition so stuff does not hang up.

 

[Terry]

I normally allow a take off of 1/4" per fitting.
So if the santee or section of pipe is 7-3/4", I would cut out 8"
The is a rubber ridge in the center of the coupling that seperates between the pipes.

 

[Jadnashua]

PVC pipe expands and contracts a lot more than CI, but generally, you can push it into the stop in the middle. I do not remember how wide that stop ridge is, but it is designed so you don't get a pocket that can trap crud. Now, it wouldn't be much, if it might let other stuff then stick to it.

A little bit extra doesn't hurt since it would then help if both ends are not cut perfectly square - IOW, part of it might be up against the stop, and the rest might not - easier to deal with than taking it all down and trying to cut an 1/8" or so more off!