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Author Topic: low temperature 'radweld'?  (Read 4076 times)
Ivan
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« on: February 01, 2015, 05:19:09 PM »

I've recently repaired a leak on our ground loop manifold - which is made up of 2" PP plastic fittings. I think the problem is that the threads are a little out-of-tolerance, and despite the large amount of PTFE used, a little movement has caused some of the fittings to swivel, and therefore start leaking.

As the antifreeze is quite pricey - given the quantity involved, I thought it would be a good idea to include some kind of additive that fills and leaky hole should it develop in the future - like the 'radweld' product that you could use with leaky car cooling systems (or egg white, which also works quite well). The problem is that the ground loop isn't even likely to get over 15C - so it won't cook the product to repair potential future leaks. Is there any product on the market that would do the job? I've seen products designed to solidify in response to drop in pressure - used to prevent tyres going flat if they puncture.
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BruceB
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« Reply #1 on: February 01, 2015, 05:48:37 PM »

Are these metal to metal, metal to plastic or plastic to plastic?
The big mdpe screwed fittings can be a bit tricky but in the past I have found masses of ptfe tape does it.
Sometimes people prefer the gas ptfe tape as it is thicker.
Liquid ptfe can also work although some are better with metal rather than plastic
http://www.screwfix.com/p/no-nonsense-ptfe-liquid/40302#product_additional_details_container

Sorry does not specifically answer the radweld question.
« Last Edit: February 01, 2015, 05:52:45 PM by BruceB » Logged
Ivan
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« Reply #2 on: February 01, 2015, 11:06:05 PM »

The leaks we had were from the PP plastic-plastic threaded fittings. The MDPE fittings with o-rings work a treat (unless you fail to push the pipe fully home, which we'd done with one pipe back in the summer). I think the problem is that we used some PP fittings from one manufacturer and some from another, and I think their tolerances were probably slightly different. We originally used lots of PTFE tape (10rolls of it on the manifolds and the various threaded connections on the ground-loop side of things in the house!!). I only had one roll of gas PTFE to hand - but we used that as well on something! I think the problem with the PTFE tape is that if the ground loop pipes are shifted relative to the manifod for any reason (eg if the manifold moves at all), it has the effect of tightening and then looseing the fittings slightly (or vice versa), and this is probably what has caused the leaks - only drips, but enough to lose pressure. The weekend before last, we had the manifold completely apart and refitted it with fresh PTFE tape AND liquid PTFE on the threads and that seems to have cured things. I think the liquid PTFE is non-setting, and will protect in future if the threaded fittings are moved slightly relative to each other.

I was thinking more of future-proofing in case we had a problem in the future, and also, if there was a product, it might make sense to put it into ground loops and solar thermal systems as standard practice. For solar thermal, I am sure you could use a rad-weld type product, but for ground loops, they never get very warm, so not sure if there is a suitable product available.
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JonG
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« Reply #3 on: February 02, 2015, 06:57:18 AM »

We have used central heating leak sealer before, on DHP-A units which have a brine circuit to an air handling unit, but no heat in them and that has worked a couple of times. We also have a bore hole system to repair in the spring where we will use the same product, we can calculate the fluid volume of the loop and add the correct quantity into the isolated section from our wheelie bin.
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camillitech
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« Reply #4 on: February 02, 2015, 07:03:23 AM »

There is a spice that's supposed to do the trick but I cannot for the life in me remember which one it is  banghead How do I know this  Huh Well many many years ago, long before the days of t'internet when I was at engineering college, my mates Riley Elf developed a radiator leak. One day he came in and proudly announced he'd fixed it, what with says I. Well he replied, it was with a spice out of my mums cupboard, which one I replied, not sure says he, I just tipped the lot in the radiator and it fixed the leak, not only that but it smells great too  hysteria

Not much help I guess really but it was hilarious at the time  Grin
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oliver90owner
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« Reply #5 on: February 02, 2015, 07:30:54 AM »

I am somewhat surprised that these plastic pipe connections rely on threads to seal.  Are these threads parallel or tapered?   If parallel, sealing will be by some other method.  Simple as that.

Options would be a)  a compression arrangement ie. an olive, either a permanent metal one or a plastic removable item, with both these alternatives utilising a reinforcing insert inside the pipe to avoid crushing, or b)  a washer arrangement, such as on washing/dishwasher machines.

Only tapered threads should be sealed with hemp or ptfe tape.  I don't think I have seen many, or any, of these for pipe connectors - maybe they may be used for the plastic outlet taps on water butts.

RAB
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biff
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« Reply #6 on: February 02, 2015, 08:54:14 AM »

 I have found,
              That down through the years,despite strict quality control,some plastic fitting and pipes vary in tolerance,however the design is supposed to be able to make up the slack, The O ring, Grab ring and washer do an excellent job.The problem sometimes is that the pipe are connected in an area that is curved and the fitting come under pressure that pulls them off square. In such circumstances the joint will continue to give trouble because the warming and cooling bring enough movement in the pipe to disturb the seal every time the temp rises to its max and goes down to its low.
  I suggest that after the next treatment of tape and solvent,you could find some way to hold the pipe firm so that the off sq.pressure is taken off the joint,allowing the O ring to perform properly without getting distorted in its seating.
                                        Biff
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Ivan
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« Reply #7 on: February 02, 2015, 10:58:31 AM »

No,these aren't o-ring seals. They're tapered threads, but as I say, I think the tolerances on the taper aren't great. (The connections to the pipework are with O-rings, but these seal perfectly). It's the actual arrangement of fittings that make up the manifold. I did wonder about solvent weld (gap-sealing variety would be best), but not sure whether it works on this type of plastic, and having called the manufacturer, they strongly recommended I didn't use it.

I'd like to know the brand of leak-sealer that JonG used - sounds like it would be a good idea to chuck some of this in the system.
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JonG
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« Reply #8 on: February 02, 2015, 11:03:22 AM »

Can I post it openly or do I need to PM you Ivan?
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desperate
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Backache stuff!!


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« Reply #9 on: February 02, 2015, 11:19:00 AM »

Plastic tapered threads?? chocolateteapot In my experience tapered threads need to be done up fairly tight to achieve a reliable seal, if it were mine Ivan I would seriously be planning to replace them with proper fittings in the summer when it can be shut down for a bit. Plastic plumbing is brilliant in the right place but that does sound shonky to me.

Desp
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BruceB
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« Reply #10 on: February 02, 2015, 01:01:34 PM »

I had a similar issue with my own heat pump in 2009/10.  I thought I would design my own filling/purging/draining valve arrangement, but with inch, inch and a quarter and inch and a half threads where both male and female were parallel threads, it really was time consuming to seal properly.

I have re-read the manufacturers' instructions and they all say ptfe tape is the way to go.  Looking at one mdpe range this morning I note that all the male threads were tapered and all the female ones parallel, which would work ok with a bit of ptfe.  The issue I had was metal lever isolation valves with parallel male threads going into plastic parallel female threads.  Not really sensible.  Potentially differential expansion also.  Although it remains today, it is on my list to change in due course. I just would not design it the same way today and would always ensure there was either a taper involved or preferably an o-ring or washer.
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Ivan
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« Reply #11 on: February 02, 2015, 10:21:20 PM »

Here's a picture of my manifolds. This was taken before we'd applied any PTFE (you can see the joints aren't screwed in very far) - my original plan was to have them underground, but having put them together, decided that above-ground would be a lot more sensible for access reasons.

My thoughts were - the pipework has to be plastic, so better to stick with plastic manifolds and plastic valves.  I suspect we won't get any more leaks from it, now we've sealed it with liquid PTFE, but I like to do things 'belt-and-braces'. I suppose I could have done it all with MDPE push-fit connectors, but it would have looked somewhat heath-robinson.





« Last Edit: February 02, 2015, 10:25:07 PM by Ivan » Logged

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camillitech
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« Reply #12 on: February 03, 2015, 07:00:05 AM »

Fraid the problem is those Italian pipe fittings from Pipestock, they may be a third of the price of a quality coupling but they are in fact carp. I have used HUNDREDS of them on all my hydro and water schemes around the croft and most of them have leaked. It doesn't usually worry me as a little drip here and there outside is of no consequence however they caused me no end of problems when used under 'negative pressure' where they were impossible to seal even with silicon (never tried the liquid PTFE right enough). In the end I swapped those for some 'Scottish Water' ones that must have been about 80 each  Shocked

Cheers, Paul
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