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Dieletric unions leaking

On our campus we have numerous research labs that have hydronic reheat coils used to heat individual offices and laboratory spaces. The Air Handling Unit supplies 55 degree air. Hydronic system piping is grooved steel and copper. Reheat piping is copper with dielectric unions when coming off steel pipe. Dielectric unions exist at pipe transitions (2", 2.5" and 3"). Also, in the summer months the central heating plant is shutdown from 9:00 pm to 4:30 am and the hydronic system cools, the piping shrinks and the unions leak (what a mess).

Many things are happening daily to this system. A suggestion was made to replace the dielectric unions with 18" sections of O2 Barrier PEX Pipe. We would like to hear the pros and cons of such an idea. Any different successful suggestions?

We certainly could use some help. Thanks Mark


  • meplumber
    meplumber Member Posts: 678
    edited June 2012
    Don't replace with pex.

    The gaskets in the dielectrics are worn and cracked. We just completed doing a school maintenance cycle where we replaced 30 something gaskets in the dielectrics on their coils. It is time consuming, but it stops the leaks.

    Or replace with brass unions. Either way works. Brass is an acceptable transition material in some areas, Check local code to make sure.
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