A no-hub coupling is used for cast iron pipe. It's a metal shielded coupling that prevents pipe shift and tightens up with a 5/16" nut driver or torque wrench.
I need to remove and replace a short section of my buried 4" CI main waste line. Seems to me I'll need the hubless couplings to slide back over the existing to allow me to place the repair piece, then slide the couplings back over thr repair piece. What couplings do I need to do this?
Will that no-hub coupling slip all the way onto the cut off pipe so that I can drop the repair piece in place, flush up against the cut-off ends, and then slide the couplings half way over the repair piece? Know what I mean? In other words, if I slip 2 no hubs only half way onto the cutoff ends, there will be no room to drop the repair piece in place right?
You can either remove or loosen the metal reinforcement part enough to get it back away from the part you're replacing, then the rubber part will be able to be folded back. Slide the new pipe in there, fold it back, slide the metal sleeve back, tighten...
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
Take off the shield and slide it onto the existing pipe, then put the coupling on the new pipe and roll it back. Do that for both sides, put in your new piece of pipe, pop the rubber onto the existing pipe, slide the shields onto the gaskets, and tighten. See the video at the end of this article for an illustration (skip to the 1:30 mark).
Also note that you don't want to cut the new pipe flush to the cut-off ends. There's a band on the inside of the coupling gasket which bridges between the two sections of pipe, and you need to account for that. I think it's about 1/2" wide - though it may be different if you're using a heavy duty coupling (not really sure).
quote; I think it's about 1/2" wide
More like a 1/16", or less.
Licensed residential and commercial plumber