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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Mechanically, PVC is rather brittle even at room temperature. Wear safety glasses if you test that with a hammer.
Combustion-wise, I think BigBad had it right. You would be dependent on not having a source of ignition. But the PVC pipe is not going to soak up liquid air, or dissolve in it, to make an explosive mixture.
Some people light PVC on purpose as hybrid rocket motor fuel. I found online examples using high pressure GOX or, much more commonly, liquid N2O (which has somewhat more oxygen than liquid air). Here's a pretty one:
-Rich
(Mach diamonds by themselves don't require vigorous combustion. Here's a cold example: .)
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
You have to be really careful with materials in contact with LOX; even fairly stable materials, particularly polymers, can leach stuff out that can detonate in mixture.
Teflon is definitely the way to go if possible, but even then there's multiple materials referred to as Teflon, they're not all fully fluorinated.
Registered Member #9640
Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26
Assuming you were able to use a plastic rather than thin-wall stainless tubing, what do you estimate the thermal load improvement would be in your construction?
I'm skeptical that this putative improvement is really significant in the larger scheme of what you're doing. If the cold reservoir is surrounded by something other than the customary vacuum jacket, a short length of standard 316SS tubing may plausibly be be a trivial loss compared to other conductive and convective losses already taken for granted, even though it's a hundred times more conductive than plastic.
This is all gratuitous commentary in light of the original chemical compatibility question, but I hope it lands close to the true information needs underlying the query.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
almost done turning out a fitting made of pure teflon to house the throttle. I've also changed out the pvc pipe for dumping the liquified gas and replaced it with a teflon tube that I made.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
IamSmooth wrote ...
almost done turning out a fitting made of pure teflon to house the throttle. I've also changed out the pvc pipe for dumping the liquified gas and replaced it with a teflon tube that I made.
Make sure you take sufficient safety precautions.
(I believe this is the first time that Carl Willis has ever agreed with me on any internet forum )
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
IamSmooth wrote ...
almost done turning out a fitting made of pure teflon to house the throttle. I've also changed out the pvc pipe for dumping the liquified gas and replaced it with a teflon tube that I made.
Be aware that teflon is susceptible to creep if held under constant pressure; fittings often need spring loading to deal with this issue.
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liquid oxygen and pvc
)