Obi-Wan
Member
I've plumbed lots of compressed air systems, but I have relatively little liquid plumbing experience. Nevertheless, I consider myself to be a more than competent DIY homeowner.
I've installed a hydronic radiant heat system in my shop. It's a closed loop system filled with a glycol mix and pressurized to between 20 psi (at rest) and 30 psi (when pumping). The heated liquid never surpasses 100F. It works well, except for two connections that I cannot get to stop leaking.
The distribution manifold from the main 1" PEX line out to all the 1/2" PEX ground loops is made of stainless steel. It has 1" FIP openings for the supply & return lines. I used brass NPT-to-PEX nipples to connect the manifold to the 1" PEX supply/return lines. See these links:
https://www.menards.com/main/plumbi...ass-adapter/646xg4pk1m/p-3289655538082578.htm
https://www.pexuniverse.com/ssm204-steel-radiant-heat-manifold
Initially, I used 3 wraps of teflon tape, just like I've always done on compressed air fittings. After a couple days of heat/cool cycles, the threaded joint between the brass nipple & stainless steel manifold started slowly leaking.
I drained the system, removed the nipples, cleaned the threads, and used 2 wraps of teflon tape plus some Rectorseal #5 thread sealant paste. Again, after a couple days of heat/cool, it started leaking through the threads. More slowly this time, but still leaking. This time, I can see cracks in the sealant paste (which is still soft), which I only assume are caused by the different expansion rates of brass and SS.
I drained & reconnected the nipples a third time, again with teflon+rectorseal, and tightened them as much as I dared. Same leaks.
What am I doing wrong? How can I stop these leaks?
Should I replace the nipples with plastic (a special order item)? It's unlikely that *both* of the brand new brass nipples that I used are defective in the same way. I don't see any deformations in the threads of the manifold.
Two other nipples in the system are plastic and screwed into copper female pipes using only teflon tape, and those are dry as a bone. Those are actually the ones closest to the heater, so they see more severe temperature extremes (but still never over 100F).
I know that the expansion rate of brass is roughly 50% higher than that of stainless steel. The expansion rate of plastic is about 3 times that of brass, although its insulation properties make it expand more slowly than metals. I would think that the more similar materials would be better. Plastic is more malleable than brass and SS, so maybe it could deform better into the female fitting?
Brass distribution manifolds for this purpose are available, but they're less common and more expensive than SS. I believe that most people are using these SS manifolds for hydronic heat systems. What am I doing differently than everyone else? The hydronic specialty retailer from whom I bought the manifold had no technicians on staff and were of no help.
I've installed a hydronic radiant heat system in my shop. It's a closed loop system filled with a glycol mix and pressurized to between 20 psi (at rest) and 30 psi (when pumping). The heated liquid never surpasses 100F. It works well, except for two connections that I cannot get to stop leaking.
The distribution manifold from the main 1" PEX line out to all the 1/2" PEX ground loops is made of stainless steel. It has 1" FIP openings for the supply & return lines. I used brass NPT-to-PEX nipples to connect the manifold to the 1" PEX supply/return lines. See these links:
https://www.menards.com/main/plumbi...ass-adapter/646xg4pk1m/p-3289655538082578.htm
https://www.pexuniverse.com/ssm204-steel-radiant-heat-manifold
Initially, I used 3 wraps of teflon tape, just like I've always done on compressed air fittings. After a couple days of heat/cool cycles, the threaded joint between the brass nipple & stainless steel manifold started slowly leaking.
I drained the system, removed the nipples, cleaned the threads, and used 2 wraps of teflon tape plus some Rectorseal #5 thread sealant paste. Again, after a couple days of heat/cool, it started leaking through the threads. More slowly this time, but still leaking. This time, I can see cracks in the sealant paste (which is still soft), which I only assume are caused by the different expansion rates of brass and SS.
I drained & reconnected the nipples a third time, again with teflon+rectorseal, and tightened them as much as I dared. Same leaks.
What am I doing wrong? How can I stop these leaks?
Should I replace the nipples with plastic (a special order item)? It's unlikely that *both* of the brand new brass nipples that I used are defective in the same way. I don't see any deformations in the threads of the manifold.
Two other nipples in the system are plastic and screwed into copper female pipes using only teflon tape, and those are dry as a bone. Those are actually the ones closest to the heater, so they see more severe temperature extremes (but still never over 100F).
I know that the expansion rate of brass is roughly 50% higher than that of stainless steel. The expansion rate of plastic is about 3 times that of brass, although its insulation properties make it expand more slowly than metals. I would think that the more similar materials would be better. Plastic is more malleable than brass and SS, so maybe it could deform better into the female fitting?
Brass distribution manifolds for this purpose are available, but they're less common and more expensive than SS. I believe that most people are using these SS manifolds for hydronic heat systems. What am I doing differently than everyone else? The hydronic specialty retailer from whom I bought the manifold had no technicians on staff and were of no help.