Dielectric Union question

SlamDunk · December 11

Hi everyone, we have a heating hot water skid on a closed loop. Thefirst half of the building was built in 2008. The second half in 2012. Both have appoximately 200 VAVs or reheat coils and all have dielectric unions connecting copper to copper. Whenever we turn off the HHW skid for maintenance and start it up again, we always have three or more dielectric unions leak in the first half of the building but never in the second half. Our thoughts are: the first half recieved a slug of defective unions.

My question is, why use dielectric unions on copper to copper piping?

Pipe sizes range from 1" to 1-1/2". Supply temp is 175; return 145.

GroundUp · December 11

Because some engineers think they know more than they do. I spent more than a year replacing every dielectric union in 7 different schools plus 2 hospitals that were all designed by the same engineer less than 5 years prior. Just get those things out of there as they begin to leak. If a union is needed, use a brass one.

SlamDunk · December 12

we have done two, with no ill effects, and are about to do a third this weekend. This engineer didn't believe in copious amounts of isolation valves, So we have shut off the heating hot water system and freeze the line.
Three hundred feet from the skid, the only isolation valve is at the reheat near the dielectric union and IT started leaking as soon as we closed it. Have to replace the valve too.

EdTheHeaterMan · December 12

" This engineer didn't believe in copious amounts of isolation valves, So we have shut off the heating hot water system and freeze the line."

Low Bid wins the contract!

Do you have a ProPress? Get valves and unions installed without worrying about water dripping on the sweat fittings. (I know … Dumb question… everybody has ProPress now)

SlamDunk · December 12

@EdTheHeaterMan No, I think between my budget conscious management, at the time, and the architects, valves and unions were value engineered out of the design.

Jamie Hall · December 12

There's no need for dielectric unions joining copper to copper. They're a nuisance anyway, and having them in that application is just silly.

Whatever you need to do, get rid of them. Put some isolation valves in while you are at it.

EBEBRATT-Ed · December 12

Has anyone ever seen a dielectric union that didn't leak at some point in its hapless life?

mattmia2 · December 12

If for some reason you needed the chassis of the appliance electrically isolated more or less from the piping system they would serve a purpose but in most cases they don't do anything a brass valve or nipple wouldn't do and on sealed systems they don't even to that.

offdutytech · December 12

Propress is your friend on jobs like that to install isolation valves. No hot work permit needed. You might want to consider renting a pipe freezing machine for a day to make the repairs. No need to drain an entire system or section of pipe. Both items will get the job done faster and save money in the end with reduced downtime.

SlamDunk · December 12

@offdutytech we have a pipe freezing machine. Just learned this afternoon that ourpro press 350 battery packs are toast. BOTH of them! This press is only two years old. It looks like they got wet. Imagine that.

GroundUp · December 12

I used to work for a company that moved one of their PMs (who was previously a secretary and had absolutely no field experience) into a VP position so he was suddenly all about penny pinching. I was running a $25M remodel job in downtown Minneapolis where we had a dual temp system feeding fan coil units throughout the building and the 8" mains ran down the center with multiple 3" branches running down adjacent corridors to serve all the units. The plan didn't show any isolation valves on ANYTHING after the boiler room so I took it upon myself to add 3" butterflies on each branch at least, during the first floor portion. Mr fancy pants VP came through one day and tore me a new one for wasting money on those valves, and made it very clear that I was NOT to deviate from the plan again. Okay then, sorry for trying to help. Fast forward about 8 months, we're up to the 13th floor and one of the brickies tears off a live 2" hot water line on 4th (everything below was now occupied) with his forklift mast. Not a valve to be found anywhere, so they dumped about 3500 gallons of water through 4 floors of office space and caused millions of dollars in damage. Building owner and mason jointly sued my company for not having valves on each floor (rightfully so) and the VP clown had the audacity to blame it on me after he had time to alter the plans to show valves. I had screenshots in my iPad as well as an extra set of paper plans in my truck to prove that it wasn't my problem, but that was also my last day working there. Last I heard, they were filing for bankruptcy- all because of a couple thousand dollars worth of valves.

SlamDunk · December 12

I guess this is more common than I thought. We have a building under construction now and a PM reached out to my boss and said the trades are concerned there isnt a shut off valve after city water comes into building from the ground. "Do you want one?". My boss said yes please. Major eyeroll. I asked if he should inquire about the backflow preventer. Nope. They'll find out during inspection😁.

mattmia2 · December 13

In AV there are a lot of people who call themselves engineers that do not actually have engineering degrees. That is usually where our design problems stem from. that and saving $3000 on equipment to later spend $5000 having to constantly support that system.

Intplm. · December 13

https://forum.heatinghelp.com/discussion/comment/1876735#Comment_1876735

Yes…I have. Until someone else came and fixed it.

SlamDunk · 5:40PM

after spending time with this dielectic union, I learned that the cpper reheat manifold stubs for supply and return are bronze or brass brazed to copper manifolds and somehow, black iron nipples are seamlessly attached to bronze stubs -which is why they used dielectric unions.

Dielectric Union question

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