Preheat tube run up centre of burner column ?

Just to throw a monkey wrench into this discussion (since I've enjoyed it thus far)…

The remote tubing is typically not made of the same material as the canisters, it is typically a plastic type of material. Given that, wouldn't there be a chance of freezing the tubing and making it brittle? Especially if it is made of questionable materials and certainly not made for the temperatures possibly encountered when propane is "boiling"?

Larry,

You're right, it's likely not the same material as the steel in the fuel canister. Maybe it's brass. But even if it's polyethylene, small diameter tubing in instrinstically very strong in burst strength.

If it's not polyethylene but some other plastic that isn't good at really cold temps, yes, wherever the propane boils will get cold. You notice that in a vapor-feed canister and from Jim's field report, it sounds like boiling is occurring in the tubing. But a plastic that gets brittle like a vinyl or PVC – it's hard to see anyone using it in this application.*

*But then I have trouble understanding why people put lead and Arsenic in children's toys, anti-freeze in wine, or artichokes on a pizza, but obviously some people do.

But even if it's metal, that doesn't mean it can't get brittle at low temps. Metal have a ductal-brittle point, hopefully quite low (like bicycle theives using liquid nirogen to break Kryptonite locks) but a few WWII liberty shattled in ocean temps.

Larry:

I was more worried about the fuel hose acting as the generator than chilling. As mentioned, the liquid fuel will expand some 200 times in volume as it changes state from liquid to gas. However as Roger, David, and Stuart have pointed out a) small diameter tubes are inherently very strong and b) there is an “out” for excess pressure so long as one valve or the other is open. Even if both valves were closed, the chances of a burst are very, very low.

Now, as to cold, that is a concern. However, most of the “big boys” (the major stove manufacturers) are using pretty quality materials. They know that BP’ing stoves are used in cold conditions. The materials available these days work pretty well even in some pretty cold weather. In addition, manufacturers are quite aware that BP’ers are on to the trick of inverting canisters. MSR just upgraded their WindPro, adding a rotating coupler to facilitate that very practice. Based on my experience, the experience of many people here on BPL as well as elsewhere, and the accumulated expertise of the manufacturers, I’m actually not too worried about the effect of cold on the fuel hose. Note that I said “major manufacturers.” Clearly some of the cheap knock offs are something to worry about.

HJ
Adventures In Stoving

> wouldn't there be a chance of freezing the tubing and making it brittle?
Certainly.
However … the hoses are typically made of PTFE, PFA or FEP with a SS braid over the outside. These are all very similar materials. Figures for brand-name stuff follow.

PTFE hoses are typically good for -450 F (-268 C) (low temp embrittlement) to 500°F (+260°C). For 1/16" bore & 1/8" OD, at 212 F (100 C) the max working pressure is 180 psi.

PFA hoses are typically good for -320°F (-196°C) (low temp embrittlement) to 500°F (+260°C). For 1/16" bore & 1/8" OD, at 212 F (100 C) the max working pressure is 190 psi.

FEP hoses are typically good for -100°F (-73°C) (low temp embrittlement) to 400°F (+204°C). For 1/16" bore & 1/8" OD, at 212 F (100 C) the max working pressure is 148 psi.

Note that 'max working pressure' includes a safety margin of FOUR times. One atmosphere is 14 psi.

Ahhhhh…. It's Good Stuff.

Cheers

>> However … the hoses are typically made of PTFE, PFA or FEP with a SS braid over the outside. These are all very similar materials.

Really? You and I may use the above for MYOG stoves, but I don't think commercial stoves use these materials. For certain, the Brunton stove stand that Jim has been using uses a black rubbery material (definitely not PTFE, PFA or FEP) for the fuel hose.

What I would be worried about are the cheap knockoffs. What do they use for the hose? I would worry that their hose could get brittle if used for liquid feed. Even if it didn't burst, it could crack enough to allow propane to escape. The fire ball that could ensue could be catastrophic.

For the quality stoves this doesn't seem to be a problem.

However, at 110*F the pressure vapor pressure of propane is 197 psi. This exceeds the working pressure of all the hoses mentioned above. 110*F is certainly reachable with just a little thermal feedback on a hot day. And while there is a large safety margin built in to the hose, it would seem that one could easily enough exceed what the stove was designed to handle.

Not that I think this is a real problem for those that know what they are doing, but I wanted to contribute something to this discussion. ;^)

What I would be worried about are the cheap knockoffs. What do they use for the hose? I would worry that their hose could get brittle if used for liquid feed. Even if it didn’t burst, it could crack enough to allow propane to escape. The fire ball that could ensue could be catastrophic.

That’s pretty much my attitude towards cheap knock offs. An imitator doesn’t know which corners can be safely cut. They have no idea how the design was arrived at or what path was taken to get there. Without that information, a corner may be cut that ought not to have been. No thanks.

HJ
Adventures In Stoving