Maximum temp of Pex tubing?

[windstuffnow]

  I've searched all over the web and have only found a couple places that rate the tubing at 200*F at 80psi.   Has anyone ever run into any data of the maximum rated temp this stuff could handle without melting down at 0 psi?

  I priced some copper tubing and it scared me so I'm looking for less expensive alternatives.  I'd like to be able to run it at temps up to 250*F. ( using a mix of antifreeze of course ).

  Any links or personal experience with the stuff would be wonderful,   Thanks in advance...

.  

 

[Kilroy2k1]

 In order to run temps that high, even with antifreeze, your still going to need to pressurise the system. In my experience the PEX gets very weak at temps over 210F, the tube itself holds its shape, but the ends where crimped come apart easy.

Tom S.

[altosack]

Well, I don't have experience with PEX delivered as tubing, but I worked as an engineer for a flexible pipe company that used PEX all the time for the pressure containment layer, so I know the basic material well.

PEX maintains full properties up to about 180 deg F; higher than that, it starts to lose its strength. As far as I know, it can only be rated at 80 psi @ 200 deg F if it is also good for at least 120 psi at 180 (just make it thicker, and it can handle a higher pressure/temperature combination, and as long as it's set in concrete or something such as in a hydronic floor, it's really no problem).

However, 250 F is well outside of its capabilities at any pressure. It will deform plastically (no pun intended) at that temperature with basically its own weight, and if I remember correctly, actually starts melting at 255-260.

The only plastic we used that could withstand 250 F was called COFLON (not sure of the generic name, but it was a variant of PVC-C), and it was around 7 times more expensive than PEX per kilo of raw material, so the copper might start looking better and better.

Best Regards,

Dave

[vawtman]

We need more info in order to be of help.

 Just givin ya crap Ed but seriosly what are you working on?Or is it undercover at this stage?

[windstuffnow]

  Thanks all, I was afraid that it wasn't going to be a simple fix but I think I can still work with it in the 200* range with less output.

  Vawtman, I'm building a stirling engine once again.  I'm trying to keep it low temp so it can be powered by the sun or by my wood furnace.  Shooting for a 50 watt low temp engine.   I would like to have the option of running it hotter but it's not a necessity for this one.

  Using copper tubing the cost would be quite high lining the hot and cold sides.   Even using it primarily for the hot end is darn'd pricey.  

  Any other thoughts on flexible tubing materials that may be available with decient thermal transfere qualities?

.

[GaryGary]

Hi,

Its sounds like Dave has your answer, but just as one more bit of data, I read an account in which PEX was used to make the plumbing connections to a solar batch water heater, and had to be replaced because it failed.

If you are thinking about using it for a solar collector, I think your best bet would be to keep the temperatures to 200F or less.  I built a "just for fun" collector from CPVC, and it did well, without ever getting so hot.

http://www.builditsolar.com/Experimental/CPVCCollector/cpvccollector.htm

Gary

[wdyasq]

KiTec tubing may work for what you want, I'm not sure.

http://tinyurl.com/yjs9lz

Ron

[pepa]

hi Ed, i am working on something like that for my boiler unit. i am building a special heat exchanger around the stack as it comes out of the boiler unit and a water cooled jacket on the cold side so i wont have a hot water line in this part of the unit. i hope to have a heat range of about 170 degree difference between hot and cold on the stirling. have you ever used a piston, rod and crankshaft from a small gas engine to build a stirling? pepa.

[windstuffnow]

  A very long time ago I used an old 5hp briggs complete minus the cam to build one.  It ran but not very well.   The engine was old and pretty sloppy but I think the rings still provided enough friction to steal a good portion of the power it was making, which was pretty low.  I made a propane burner for it and was able to get some good heat into it.   It would top out at around 200 rpm and you could easily stop it by grabbing the shaft with your hand.   It was pretty cobbled together and wasn't one of my best works.  

  Thats about what I'm looking at for a temperature difference, 150-200 degree between the hot and cold.   I'm using a 12 inch power piston on this one, I think it will work well but I'm not sure of the life span at this point.

  Run it till it quits and redesign the part that failed....

.

[pepa]

thanks for the reply Ed, i follow all of your work with interest. papa

[kenputer]

I " used" to use kitec for all my infloor and baseboard heating systems but  had the layers seperate at a joint and the manufacturer said the boiler must have been set at over 220 deg. for that to happen and they would not back the product, So kytec is not a good idea.

Ken

[wdyasq]

Thanks Ken,

Ron