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Leak between brass fitting and stainless steel manifold

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Obi-Wan

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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:



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.
 

Obi-Wan

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toss the Teflon tape out the window
you most likely wrapped the threads backwards.
No, I've been sealing tight air fittings for decades. I can do teflon tape correctly in my sleep. It's wrapped the right way.

use the recto seal with out the teflon tape
i use pro dope for hard to seal threads
I'm willing to try anything (cost permitting), but what is the teflon tape doing to cause these leaks? What makes one type of sealant better than another?

I'm getting pretty tired of draining and re-pressurizing this system every time I have to fix these leaks.
 
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SHEPLMBR

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No, I've been sealing tight air fittings for decades. I can do teflon tape correctly in my sleep. It's wrapped the right way.



I'm willing to try anything (cost permitting), but what is the teflon tape doing to cause these leaks? What makes one type of sealant better than another?

I'm getting pretty tired of draining and re-pressurizing this system every time I have to fix these leaks.
the glycol will break down the white teflon. as with pipe dopes, read labels and make sure u can even use the dope with a glycol system.
 

Obi-Wan

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the glycol will break down the white teflon. as with pipe dopes, read labels and make sure u can even use the dope with a glycol system.
Interesting. The label from that white teflon is long gone, and I don't remember seeing anything on the glycol bucket or the dope tube that indicated they were incompatible. The dope specifically says that it's safe for all kinds of different stuff. I'll go out & double check later today. This is a propylene glycol mix that's made specifically for radiant systems, not ethylene glocol like you use in your car.

I haven't had any trouble with the other four threaded fittings in this system leaking, and they're all sealed with nothing but white teflon. It's just these two on the manifold that are giving me problems.
 

SHEPLMBR

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Interesting. The label from that white teflon is long gone, and I don't remember seeing anything on the glycol bucket or the dope tube that indicated they were incompatible. The dope specifically says that it's safe for all kinds of different stuff. I'll go out & double check later today. This is a propylene glycol mix that's made specifically for radiant systems, not ethylene glocol like you use in your car.

I haven't had any trouble with the other four threaded fittings in this system leaking, and they're all sealed with nothing but white teflon. It's just these two on the manifold that are giving me problems.
Maybe you have a cracked fitting. n Seems like you are doing the same thing over and over, to no avail.
 

frodo

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I looked at your manifold. It is SS but i do not believe the tee and valves are, scrape the valve body with a knife blade. It looks like it has been cast

toss the adapter and use another.
 

Obi-Wan

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Maybe you have a cracked fitting. n Seems like you are doing the same thing over and over, to no avail.
Cracked where? The leak is coming out through the threads. When I clean out the threads each time, I don't see any indication of damaged threads or fittings.

I haven't done *exactly* the same thing each time. I'm running out of ideas for what to tweak, though.
 

Obi-Wan

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OK, I ran out to the shop to look at stuff.

The manifold now has several knife scratches and pipe wrench dents, and they're all silver. If the manifold is plated, it's really deep. I believe that it's solid SS.

The bucket of Cryo-Tek glycol doesn't say anything about incompatibility with any sort of pipe sealant. It does say not to use it with CPVC pipes.

The tube of Rectorseal 5 says that it's formulated for "a wide variety of fluids and gases." Only oxygen, chlorine, and other oxidizers are prohibited.

I don't see any problems with any of that stuff as it currently stands, unless the expansion rate of the stainless steel manifold is causing issues.
 

Mitchell-DIY-Guy

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Let me interject a couple of items here, take them for what they are worth.

1. Glycol, either PG or EG (assuming you have an EG system, but I don't know that for certain) will not break down PTFE (Teflon). It is one of the most resistant (to solvents, acids, organic compounds, etc.) plastics known.

2. Sad to say, the quality of "those pre-made SS manifolds" is suspect. So, you may have, quite simply, a hairline crack, defective threads, or something similar. Those manifolds are sold by a variety of people, most are unbranded, most are made in China. You can find them on eBay, Amazon, and any number of places.

When I designed and built a driveway de-icing and snowmelt system for my home back in 2009, I originally bought a set of these manifolds, but after careful examination of the quality, and a little investigation into the flow rates, determined the quality was not good enough for me, and the valving on each branch added a flow restriction. That might be OK for indoor radiant heat application, but was wholly unsuited for a snowmelt system, where flow is far more critical and essential.

So, I went about to design my own manifolds and was lucky to have found a custom manifold manufacturer, Alberta Custom Tee in Canada. I specified the size of the piping, and the size of the stub-outs, and the spacing and size. They fabricated everything exactly to my needs. They had a USA sales rep, and I went through the sales rep. Took a couple of weeks for fabrication and the price, though lost to memory, was reasonable. Alberta Custom Tee (2006) Ltd, Copper Manifolds, Headers & Tees They appear to have changed their name, but that's the same firm. There's a very cool machine that fabricates the tees, and another that brazes (not solders) the stubs in place.

I've never been a fan of fittings that require specialized tools (like crimpers, etc.) so I decided that what I would want is conventional NPT screw fittings. To that end, I needed to source proper valves for the manifolds. Quite interestingly, once again I turned to my neighbor to the north, and found Dahl Valves. Home | Dahl Valve Limited Also once again, I went through a USA sales rep, and ordered the requisite valves. They are modular, so you choose the valve body, then the input and output fittings. Well, upon recommendation of my installer, I specified ⅝" PEX Compression fittings on one end, a needle valve flow adjustment, a shutoff, and a dead swivel FPT on the other end. The valves are FULL FLOW, a complete, un-impeded ½" inside diameter of the copper tube and the inside of the PEX. These valves, too, were reasonable in price and all brass; if I remember the cost they were about $16 each. See the photo of the return manifold. Supply manifold identical EXCEPT the handles are red instead of blue.

The good news for you is your leak is NOT at one of the ports; that would be a "time to toss it in the trash" kind of problem. Your leak is on a replaceable part. So, replace that input part. If you search and you are lucky you may be able to find a single SS valve with the same dimensions and the thermometer port. If not, you may need to cobble together something with some fairly common SS parts. Worst case you may find someone selling one of these manifolds (doesn't matter the size, really...) used on eBay or something, and you can salvage that valve.

Interestingly, my driveway snowmelt system, fired by a 199,000 BTU Takagi TK3 heater in a "primary loop/secondary loop" system, was never pressurized beyond what pressure might be created from heating the fluid and pumping. In other words, at "rest" when "cold" it was at atmospheric pressure. We heated the primary loop to about 140 or 158 degrees; I didn't want to run anything at its upper limit. Flow rate through the heater was about 5 GPM, and in the secondary loop, about 30 GPM. I used a custom mix EG fluid from Kost KOSTChill™ Heat Transfer Fluids - KOST USA, Inc. - Cincinnati, Ohio at about 40% concentration. I think that was fine for the climate I was in.
 

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frodo

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I see your insulation is not installed properly
use contact cement on the edges and seal the insulation around the pipe
on fittings. miter 90's and saddle tees.
 

Mitchell-DIY-Guy

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Thanks for the advice, @frodo but the insulation was because I had it around--not because it needed it. There's 2,000 feet of PEX in that installation, and the only exposed that could theoretically be insulated is the short pieces you see, just a few feet. The rest is buried in concrete. There's no room for any insulation around the valves or on the manifolds, because the distances are so tight. The only way to have insulated all of that would have been to use spray foam.

Sold the house in 2019, but regardless as you can see from the photo the system worked well enough
 

Obi-Wan

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So it's been a week since I last checked in. I replaced the brass 1" PEX nipples with plastic (poly) nipples. I used white PTFE tape and Rectorseal 5 dope on the threads, just like I'd done before on the brass fittings. The plastic ones were able to thread into the stainless steel manifold a good two turns farther than the brass nipples did.

I left the system dry and let the dope cure for a day, then pressurized the system and let it heat for a couple days, then turned it off and let it cool down for another day (when is when the leaks used to form), then turned it back on for a couple days. The connections are still bone dry, so I think it's safe to declare my problem solved.

Either those brass Sioux Chief nipples were out of tolerance, or the SS manifold was out of tolerance and the plastic NIBCO nipples were soft enough to deform around the SS threads to make a decent seal. Either way, we're finally cleared for takeoff. Thanks for the advice you all provided.
 
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