How can I make a water tight seal?

[BoomTown]

I want to use a 3” PVC wrapper around 1 ¼” Copper to creat a water jacket. How can I make it water tight where the copper goes in and comes out of the PVC?

[still_stirrin]

Probably, you can’t. The materials have different coefficients of thermal expansion. Always gonna’ leak.
ss

[Kindafrench]

Thick lids for the pvc pipe with a tight fitting hole for the copper pipe and epoxy glue?

Or some kind of compression fitting with o-rings.

Bigger diameter water outlet than water inlet could avoid pressure in the system and keeps it better
from breaking. Let the water flow as free as possible.

Don‘t know if my ideas are explained well. Have to get more coffee.

Anyway. It might be better to avoid this special design and rethink it.

Why pvc and not copper? Why this design? How long? Diagram, please.

[NZChris]

At the bottom, most flexible sealants should work.

Design the top end so that it isn't sealed and expansion differences aren't a problem. I've been running a Liebig that isn't sealed at the top for over thirty years. When I can't hear it's siphon sucking air, I know I have a problem.

[Yummyrum]

Use Silicone sealer ... it will stick like shit to a blanket and is flexible so different heat expansion issues won’t matter .
Just make sure the silicone is fully cured before you test it with water .

[cob]

Because i have the tools milling the caps to accept o-rings comes to mind.

having said that once you solder fittings to the 1.25 copper, any kind of

interface between the copper and PVC becomes effectively unserviceable.

[SmokyMtn]

Not sure it would take the heat. But look for a pvc "dresser" coupling. Cut the pvc to length, glue male adapters on the ends. Use the gaskets and ends off of the coupling. I would check that the threads match before buying. I'm not positive

[BoomTown]

Ok, I give up...surely there are plumbers that know how to do this, but I’m falling back to copper in copper...

[Butch27]

Does it have to be PVC? Would ABS drain pipe work? If so have a look at the connector that goes from the metal tailpipe on a bathroom sink to the ABS trap. It is a gland nut type fitting that tightens the seal as the nut is tightened. I think it may be close to the 1 1/4 that you want to use. You may be able to leave it loose enough to move with expansion, yet tight enough that it will not leak.

[RC Al]

Use Silicone sealer ... it will stick like shit to a blanket and is flexible so different heat expansion issues won’t matter .
Just make sure the silicone is fully cured before you test it with water .

This - just use a silicone that is heat resistant - just go to you your large hardware and start reading labels, top of the condenwsr shouldnt get much more than 212. NZchirs's solution has merit too - but I would prefer sealed my self, we have tank water and every drop is precious.

Ok, I give up...surely there are plumbers that know how to do this, but I’m falling back to copper in copper...

A plumber would have zero clue, this is a heat exchanger, not a toilet

[Zeotropic]

Use Silicone sealer ... it will stick like shit to a blanket and is flexible so different heat expansion issues won’t matter .
Just make sure the silicone is fully cured before you test it with water .

This - just use a silicone that is heat resistant - just go to you your large hardware and start reading labels, top of the condenwsr shouldnt get much more than 212. NZchirs's solution has merit too - but I would prefer sealed my self, we have tank water and every drop is precious.

Ok, I give up...surely there are plumbers that know how to do this, but I’m falling back to copper in copper...

A plumber would have zero clue, this is a heat exchanger, not a toilet

Any 100% silicone should do nicely as it can handle close to 600°f. I buy mine at ace hardware in a squeeze tube.