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Old 10-12-2009, 03:03 PM   #1
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Pex Tubing Airlock


I put in radiant floor heat in my entire house using pex. I have an outdoor wood burning furnace that heats all the house and garage. Last year I put in a cement driveway and put pex in that just like the house. It is all done correctly. The driveway is 8 loops with about 200-250 feet per loop. In the house I put a bleeder valve at the top of each loop but I couldn't do that in the middle of the concrete. The house is just water but in the loops in the concrete will be water/antifreeze. My problem is when filling the tubes outside with a sump pump (and other pumps I've tried), it only fills the tube, 1 loop at a time, about 30-50 feet and then stops. The driveway is on an incline, that is why I did the tubes, but I am sure it is airlocked somewhere in the top part of the loop. I have a bleeder valve on the end of each loop just before the manifold but nothing comes out. Is there a vaccuum type pump to put on the other end of the loop to suck out the air while I am pumping fluid into the front end? It is getting cold and snowy out so I am trying to fix this soon. Can anybody help? All 8000 feet in my house/garage work perfectly with no problems at all. Thanks. Matt

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Old 10-12-2009, 03:55 PM   #2
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I don't think you could airlock and open loop. Fluid would seek the lowest level pushing the air higher on either side of the loop. What is happening? Is the pump stalling? I just can't picture exactly how you are filling this tubing.

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Old 10-12-2009, 06:45 PM   #3
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I put the water/antifreeze in a bucket and set the sump pump in it and turned it on. I also tried a pump you put on a drill. It sucks the fluid and pushes into the 3/4" fill tube that runs about 20' until it hits the manifold/loops. It may not be airlocked, in the sense that it has fluid on both sides, maybe just too much pressure for the fluid to push the air out?
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Old 10-12-2009, 06:54 PM   #4
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I am wondering if when I pump the fluid in, it compresses the air and then it can't force it out. I am not sure exactly what is happening. I just start the pump and it pumps for a minute or 2 and then it will not pump anymore. The pump works fine otherwise, I have tested it. I also tried hooking it to a water spigot on the house and it fills it the same distance and then it stops, just like the pump. The air is not coming out the other end. That is why I am wondering if there is a vaccuum type pump to suck the air out the other end while I am filling the front end. Hopes this helps you to see the situation.
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Old 10-12-2009, 07:09 PM   #5
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Quote:
Originally Posted by mattlen View Post
The air is not coming out the other end..

does any air ever come out the other end? If not, I would suggest something happened to your tubes and they are closed off.

Try simply pumping air through the tubes. They should flow easily.


You might also try filling from the bleeder end. (might have to rig something up). If you fill the topside of the tube, the fluid should simply run out the bottom end.
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Old 10-12-2009, 07:19 PM   #6
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Let me try this explanation. The in and out manifolds are at the bottom of the driveway. The tube goes about 50' up the driveway (this is about a 6' vertical incline to the top of the driveway by the garage), then levels off and runs about 100' through a sidewalk etc., then descends back down 50' or so to the out manifold at the bottom of the driveway. Hope this helps.
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Old 10-12-2009, 08:39 PM   #7
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I suggest that you rig an air compressor to one tube at a time.If the compressed air passes -your pump is probably cavitating.

If compressed air will not pass through the pipes--They may be crimped some where.

I can not imagine ALL the tubes got crushed. Try the air and let us know.
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Old 10-12-2009, 10:05 PM   #8
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I know these are obvious but I have been known to miss the painfully obvious before so let me throw them out:
1. If there is a valve on the outlet manifold check to be sure it's open.
2. Check to be sure the fluid level in the bucket isn't too low for the pump to pick up.
3. If the sump pump has a float switch check to be sure it's not cutting it off.
4. Maybe the tubing diameter and length/height is creating too much head pressure that your sump pump can't handle (might be showing my ignorance about sump pumps here but they usually have a large outlet pipe)
5. Why not try the real radiant pump that you'll use in the application?
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Old 10-12-2009, 11:10 PM   #9
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I have tried the pump that will be pumping the fluid and it can't push it any farther. As far as putting air through the tubes, that may be it but I highly doubt it. I have tried putting fluid through all of them and they are all the same. I poured all the concrete myself and know nothing was done b/c I was pressurizing it at the time. I know they weren't crimped. I think #4 above might be the ticket, too much head pressure for the sump pump. Do I need a bigger pump to fill the tubes? The pump I have to circulate the fluid should be good enough but I can worry about that once the fluid is in the system.
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Old 10-13-2009, 12:04 AM   #10
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Originally Posted by mattlen View Post
I have tried the pump that will be pumping the fluid and it can't push it any farther.
So, since you are presuming the lines are fine, has this made you realize the pump you now have is not larger enough?



So, when you pump any fluid in the lines, does ANY air come out of the bleeders? If not, you have a problem. Air should come out any time you put any fluid in the lines.

In a previous post, you pondered the possibility the air was being compressed. If you have the bleeders open, there would be no pressure. As I stated, the air would simple bleed out.
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Old 10-13-2009, 12:42 AM   #11
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IMHO, the sump pump will not work because they will not pressurise when reduced down to small tube size. you will need a pump like this to do the job http://www.amazon.com/Wayne-PLS100-P...838301-3108032 either pump the fluid into the system or suck it into system. I use these to suck antifreeze in to buryed waterlines for winter close downs. put antifreeze in 5 gal bucket let pump suck it into system.

should work without a hitch, hardest part will be getting hooked up. the pump you will use on the system is just a circulator pump it will not pump/fill the system. will you have a resavor to hold antifreeze to replace any evaporetion that will occur over time?
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Old 10-13-2009, 08:55 AM   #12
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Since this is basically an open system until all the air is out, it sounds like the pump doesn't have enough head to push by the high point in the system. Once all the air is out and the system is closed, it will probably work fine until the next air lock.
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Old 10-17-2009, 09:57 AM   #13
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Dear Mattlen:
Please post the outcome of your situation.
I am highly curious to find out what was the cause of your predicament for I am considering doing a hydronic radiant heat driveway myself.
I am looking for all information to prevent any unfortunate incidents such as yours and things like cracking.
Can you tell me any of the particulars in the process your driveway contractor used such as substrate material and thickness and the thickness of the concrete.
I am looking to put in concrete with the tubes and then pavers on top.

Thanks .... hope you have much success with the outcome.

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