leaking unions...

bhurst

We are having a problem with unions leaking in a heating water system.  What we have is a heating water loop with packaged RTU's and VAV re-heat.  What happens is, the boiler will shut down periodicaly but the loop pumps do not.  Therefor we are now circulating water through the package units cooling the water down to around 70*F or less.  When the boiler is brought back on line, our water then reaches the set temperature during the summer of 145*F.  Once this happens, we start to have leaks on our Griswold piping packages at the VAV boxes and the di-electric unions on the RTU's hot water coils.  So we re-tighten the fittings and next time the boiler shuts down, we have to go back and tighten some of them again, or different ones again.

What could be causing this?

Ron Jr._3

Any chance

of taking those dielectric unions out of the system ? Sounds like its a package type of system , so probably not ?



I'd use a soft setting thread sealant on the union faces . We have periodic leaks on steel unions ( steam mainly ) , and that does the trick every time . We use Teflon based sealant for this problem .  

Tom Blackwell_2

Removal

The only fix for this is to remove the dielectric unions. In real life the dielectric unions serve no purpose except another place to leak. The reason they don't work is this-the dielectric joint is supposed to isolate stray current caused by different metals being in the same conductive flow path; since both sides of the dielectric are grounded to the building structure in some manner. A much better solution is to use a bronze gate or ball valve as the dividing point. This is what we no do, except when we encounter a stubborn AHJ who wants them even if they leak. We are now in the process of reworking a building we did 8 years ago with about 300 coils-the majority have had leaks at the dielectrics.