Anyone ever tried PEX tubing with biodiesel?

Anything related to biodiesel/biofuels, questions, answers, technical information for all VW Diesel Engines should go here.

Moderator: Fatmobile

Post Reply
Krank
Diesel Freak
Posts: 171
Joined: Wed Jul 05, 2006 10:49 am
Location: Hillsboro, Oregon

Anyone ever tried PEX tubing with biodiesel?

Post by Krank »

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?
'81 Rabbit N/A
'82 Audi 4000 Diesel (a vw in luxery clothing!)
Pu241
Cetane Booster
Posts: 50
Joined: Fri Aug 10, 2007 6:24 pm
Location: Bridgeport, OH

Re: Anyone ever tried PEX tubing with biodiesel?

Post by Pu241 »

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.
All problems can be solved with the appropriate application of antimatter!
'81 Rabbit 125K
'88 GMC Step Van P-30 6.2L
Detroit Diesel 2-71 Generator
Krank
Diesel Freak
Posts: 171
Joined: Wed Jul 05, 2006 10:49 am
Location: Hillsboro, Oregon

Post by Krank »

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.
'81 Rabbit N/A
'82 Audi 4000 Diesel (a vw in luxery clothing!)
Pu241
Cetane Booster
Posts: 50
Joined: Fri Aug 10, 2007 6:24 pm
Location: Bridgeport, OH

Post by Pu241 »

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
All problems can be solved with the appropriate application of antimatter!
'81 Rabbit 125K
'88 GMC Step Van P-30 6.2L
Detroit Diesel 2-71 Generator
Krank
Diesel Freak
Posts: 171
Joined: Wed Jul 05, 2006 10:49 am
Location: Hillsboro, Oregon

Post by Krank »

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.
'81 Rabbit N/A
'82 Audi 4000 Diesel (a vw in luxery clothing!)
Pu241
Cetane Booster
Posts: 50
Joined: Fri Aug 10, 2007 6:24 pm
Location: Bridgeport, OH

Post by Pu241 »

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!
All problems can be solved with the appropriate application of antimatter!
'81 Rabbit 125K
'88 GMC Step Van P-30 6.2L
Detroit Diesel 2-71 Generator
Krank
Diesel Freak
Posts: 171
Joined: Wed Jul 05, 2006 10:49 am
Location: Hillsboro, Oregon

Post by Krank »

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.
'81 Rabbit N/A
'82 Audi 4000 Diesel (a vw in luxery clothing!)
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Post by Fatmobile »

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.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
surfcam
Turbo Charger
Posts: 1482
Joined: Tue Sep 28, 2004 8:43 pm
Location: Canada Southern Alberta
Contact:

Post by surfcam »

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.
99 TDI Jetta (Z1 engine code)
94 Grand Caravan
89 Dodge Gold Stream B class
http://www.antiquedollhouseofpatterns.ca/
odie
Cetane Booster
Posts: 61
Joined: Thu Aug 06, 2009 12:20 pm
Location: CC, TX

Post by odie »

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.
1981 VW Caddy with 85 diesel Jetta motor
1987 MB 300TDT diesel
1983 D50 Ram 2.3TD diesel
1985 Isuzu Pup 223 diesel
1983 RV 6.2 TD diesel
1983 Maxima diesel (sold) :-(
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Post by Fatmobile »

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.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
odie
Cetane Booster
Posts: 61
Joined: Thu Aug 06, 2009 12:20 pm
Location: CC, TX

Post by odie »

oops :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.
1981 VW Caddy with 85 diesel Jetta motor
1987 MB 300TDT diesel
1983 D50 Ram 2.3TD diesel
1985 Isuzu Pup 223 diesel
1983 RV 6.2 TD diesel
1983 Maxima diesel (sold) :-(
Fatmobile
Global Moderator
Posts: 7564
Joined: Wed Oct 30, 2002 10:28 pm
Location: north central Iowa

Post by Fatmobile »

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.
'91 Golf gasser converted to a 12mm pump, M-TDI.
'84 1.6TD Rabbit with a VNT-15 turbo, still setup to run on vegetable oil.
'84 GTI with 1.7TD pistons and intercooled.
2003 TDI wagon
2000 TDI Jetta.
dalemonroe
Glow Plug
Posts: 1
Joined: Thu Jun 20, 2013 11:57 am

Re: Anyone ever tried PEX tubing with biodiesel?

Post by dalemonroe »

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.
surferdean
Glow Plug
Posts: 4
Joined: Sat May 03, 2014 4:11 pm
Location: Santa Barbara, CA, USA

Re: Anyone ever tried PEX tubing with biodiesel?

Post by surferdean »

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.
1982 VW diesel 1.6L NA caddy pickup
328,000 + miles daily driver
7 yr. 52,000 mi. on WVO
Post Reply