Tying PVC to cast iron question...

[mailman62]

Planning on connecting to 4 in cast iron , what type of coupler would be best, can I use a 4in rubber coupler , or a no hub coupler which has the metal shield around it, this would be located in a crawl space

 

[Cacher_Chick]

The unshielded coupler is for below grade (buried) use only.

 

[Sponsor]

 

[mailman62]

ok i have a choice of either cutting the small sec of cast iron pipe and using 2 shielded couplers , or using 1 shielded coupler on one end and run the pvc to the next cast iron joint, question is the rubber seal that goes into that , how does it seal ? seeing that there are no bands to it like the shielded coupler

 

[Terry]

If you are talking about inserting plastic into a cast iron hub, with a rubber donut, then you will need to shove that end in.
If you intend to cut into a line and place a section within, then the no-hub style couplings allow you to do that.
The metal wrap prevents the pipe from sagging at the joint. I've seen some pretty badly deformed rubber couplings that homeowners have tried to use. It may take a few years, but it can look pretty bad after a while.

 

[mailman62]

sure that makes sense on the possible sag on the rubber coupling, with the rubber donut is it as simple as just inserting in ci then inserting pvc , nothing else ?

 

[Cacher_Chick]

The rubber donut must be sized to the i.d. of the hub on the c.i., as there is no one standard size.

 

[Jadnashua]

The CI pipe's hub is not a standard size - it can vary foundry to foundry and whether the pipe is 'standard' or heavy duty. They make numerous donuts. The pvc OD is standard, but you need to get the OD of the donut the proper size or it will either be too loose and leak, or be too big and a major pain to be able to insert the pvc, if you can get it in at all once the hub compresses things. As said...to get the right fit, you have to measure the ID of the hub, and get the right one which you might have to special order if you're not lucky. Since CI is heavy, an area may only have stuff from one foundry, and the sizes might be known and the supply house might have the one you need, but it's not guaranteed. It can vary by age, too, so that's not a given, either, which is why they make lots of incremental sizes of the donuts for each size of pipe.

 

[Terry]

The rubber donut must be sized to the i.d. of the hub on the c.i., as there is no one standard size.

I try to have several different ones on hand, just in case. Cast over the years has had different sizing.
With the no-hub style, I sometimes need to use a copper by cast no-hub for the transistion. If the OD is something like pipe size plus 1/8", that's a copper size.