Former VWDieselParts.com Forum

I've never even handled PEX yet, so I'm a little disadvantaged. I don't yet know exactly how flexible the stuff is. What I do know is that it's Polyethylene, which is known to withstand biodiesel, and that it's supposed to be able to deal with hot water due to the molecular alignment and bonding. I would presume that since the temps I deal with when I cook a batch of bio are similar to those of house hot water, this might be a workable material in my reactor system.

I'm planning on trying and testing, unless someone here can give me advise that would make me rethink this whole idea.
Any input?

PEX is cross-linked Polyethylene it is a 3 dimensinally bonded polymer like a car tire. It is not as flexible as vinyl tubing and may have some crimping issues. But, as it is used in "infloor" hydronic heating systems there must be ways to connect it to itself and manifolds for hot water distribution. It should withstand both biodiesel and hot water but how hot I'm not certain at this point.

Since a water heater should be able to easily achieve 140 deg f, I would expect that 130 to 140 f with bio should be an achievable standard. For my processor, I don't expect to need flexibility... structural rigidity is actually a plus. The question would then fall to whether sharkbite fittings can handle the biodiesel. I'll be running some tests unless someone can tell me not to bother.

No it isn't polyethylene any longer it is crosslinked meaning its molecular structure bears the same relationship to polyethylene as graphite does to diamond or natural rubber does to a cured tire. Similar monomeric units completly different bonding structure!


Google is a wonderful tool:

http://www.biodieselnow.com/forums/p/68 ... aspx#49872

http://www.plumbingsupply.com/polyb.html

its molecular structure bears the same relationship to polyethylene as graphite does to diamond or natural rubber does to a cured tire

You have a way of showing me the light! I definitely feel I have a better understanding of the material after reading this. I'm not seeing anything yet that would make me think this might not work, so I'm planning on delving in and running some trials.

Krank wrote: You have a way of showing me the light! I definitely feel I have a better understanding of the material after reading this. I'm not seeing anything yet that would make me think this might not work, so I'm planning on delving in and running some trials.

I wasn't trying to disuade you from using PEX, I just think you should be made aware of what you are using. As all materials have there strong and weak points, but for this application I think PEX will be fine.

As far as "showing the you the light", best I can do is maybe an anology.
Polymers are long chain molecules much like spagetti, but very much thinner and longer proportionately. Now like cooked spagetti that has been stirred-up and drained its very difficult to remove a single stand because of the entanglement of the individual strands. This is a normal polymer, polyethylene if you like. Now think of some means of linking the individual strands together, not end to end. Now it will be impossible to remove a single polymer strand. Because the entire mass is linked together. This is a crosslinked polymer. Depending upon how much the polymer is crosslinked will determine a materials chemical and physical properties.
Hope this helps, I'm not a very good professor!

I got around to checking out the PEX. Wow. That won't work in my system. It might be compatable, but criminy it's stiff! That defeats the whole intent! Nope. Not using that.

I've used PEX for a long time and have taken some prettty sharp turns with it.
Damn hard to kink it.
I did have it collapse under high vacuum.,... switched to vegy in very cold weather and didn't check the vacuum gauge until it was stumbling.

I used a tool that I bought for crimping my CV boots on. You have to buy the clamps that have the two little dimples on them. Theirs a third leg on the tool that makes the crimp more of a mushroom shape. I took that part off and the crimps seem to be tighter. The other tool for doing the round crimps is more pricey and only does one size. Its niece to have the tool when you have time to do the job.

DO NOT USE PEX WITH A HEATED SYSTEM.

i used PEX when i built my first WVO system on my old Mercedes. I ran pex inside 3/4 heater hose for a HIH hose-in-hose heat exchanger off of my radiator system. it melted the PEX after a short with.

My first setup melted too,..
when I used poly tubing.

It has never melted with PEX, even when the engine has gotten hot. I put it in boiling water and it didn't even get soft.
odie, I think you used poly,... like "From the fryer to the fuel tank" suggested.

oops you are right...i did use poly... and it melted.

I did a test later with PEX. it did not melt but got very soft...to the point that you are going to have joint failures with PEX in my opinion.

i ended up using copper inside 3/4 heater hose for heating my WVO.

I do put stents inside PEX,
wherever there is a compression fitting.
I think it does get soft enough to pull away from the o-ring I use for a seal. That stopped any leaks.

I've installed PEX tubing as fuel line on my 06 Sprinter. After installing an extra tank in the rear, the fuel pressure was not adequate. The 1/2 inch PEX allows freer flow of the thicker than petro biodiesel.
I have been soaking PEX tubing in biodiesel for over a month now and it shows no softening or sloughing. I used PEX fasteners and appropriate crimp clamps adapted to 1/2 inch pipe threads and back to stock 5/16 ID tubing. I read that copper lines were not compatible with biodiesel.
Also of interest, I bought biofuel compatible rubber tubing and found that only the inside layer of rubber was bio compatible. Biodiesel dissolved the outside and left my hands black. After soaking in bio, I swabbed the inside with a Q tip and it came back clean. This hose was a major brand, Gates I think.

I installed a 2 tank WVO system in my 1982 VW 1.6L diesel pickup 7 year ago using clear polyurethane tubing. I have had no problems. It is easy to get and not expensive. And now, it has withstood the test of time. In fact part of my WVO heating system has the polyurethane tubing co-axially inside a coolant hose with no problems in this harsh hot condition.