Ram Promaster Forum banner

21 - 28 of 28 Posts

·
Premium Member
Joined
·
1,733 Posts
Yes, I think you are right.
So, it looks like vapor pressure of propane gets up to atmospheric pressure a bit lower than -10F.

A now puzzling thing for me is that we have propane heat in our home and some of the piping and the regulator are outside in the air, and we have (rarely) seen -30F and our propane furnace continues to operate (thank goodness!).
Our tank is underground, but some of our neighbors have above ground tanks and I've not heard of anyone having a problem. Maybe the thermal mass of the tank keeps it from getting down to the low temperature.

I can remember from climbing days taking our butane stove into the sleeping bag so it would work in the morning :)

Gary
 

·
Premium Member
Joined
·
1,733 Posts
Hi,

Actually we got that wrong...

The charts on this page give the absolute and gage vapor pressures for propane

At -44F (boiling point of propane), it produces 14.7 psi (one atmosphere) of absolute pressure and 0 psi gage pressure.
By about -30F its up to 20 psi absolute and about 6 psi gage.

So, its going to be hard to get propane cold enough where it won't produce enough pressure to work -- unless its contaminated with water or something else.

Gary
 

·
Registered
Joined
·
1,556 Posts
Hi,

Actually we got that wrong...

The charts on this page give the absolute and gage vapor pressures for propane

At -44F (boiling point of propane), it produces 14.7 psi (one atmosphere) of absolute pressure and 0 psi gage pressure.
By about -30F its up to 20 psi absolute and about 6 psi gage.

So, its going to be hard to get propane cold enough where it won't produce enough pressure to work -- unless its contaminated with water or something else.

Gary
Of course we like 29.92 inches Hg over 14.7 psi
 

·
Registered
Joined
·
1,556 Posts
I thought you guys liked 760 mm :)

Gary
😜

I was in school during the Canadian Metric Conversion in the 70’s 🙄. I think it is like knowing 2 languages. Metric of course is way easier as it relates to our world with science & has easily usable decimal points. It is easier to to just forget about imperial but the real world does not work like that - go to the lumber store and ask for a straight 38x89 DF#2 or better or a 1220x2440 sheet of standard 18 non T&G and see the look you will receive from the yard guy.

My understanding is you have had a career in aviation, I am just a hobbyist. Inches of mercury, knots, fahrenheit, gallons, pounds, etc & converting fluently at the design table into metric or whatever else needs conversion is one thing; sitting in a cockpit with busted fuel gauges chatting French & English Metric & Imperial converting fluently is also no problem (providing you are an expert glider pilot);


The story of this fascinates me as life is sometimes way way stranger than fiction.

I always enjoy reading your scientifically presented posts Gary. IIRC it was RD who once wrote you are an invaluable gem of this Forum @ I could not agree more !!

I have not had problems with my propane (van heater or other propane equipment) or my cheap Chinese cabin diesel heater yet both operating at 6000’ “Density Altitude”. I believe “True Altitude” is irrelevant in regard to fuel combustion & what really matters is “Density Altitude”. IIRC @MsNomer set her Wabasto heater to “high altitude” & keeps it on that setting even when at lower elevations. The burners tend to clog up on these units & I would probably operate the same as her if I had a Wabasto changing elevations. Not having a Webasto manual I do no know if they talk about “True” altitude or “Density” altitude, nor do I know if they have more than 2 altitude settings. My rambling point is this; propane or gas or diesel what really matters to your oxygen combustible appliance is what “density” altitude you are at. Have operated @ 6000’ DA when the TA is only 3400’ (the swings can be that great).
 

·
Registered
2014 136” HR
Joined
·
4,849 Posts
My Webasto does not have "altitude" or "density" settings. It has a rheostat with numbers 1-7. If the high altitude procedure is performed, the unit will perform better at higher altitudes—no precise numbers given. Tech Webasto told me that it is not a simple reverse procedure to reset to lower altitude. If I were to mess with it again, I would need someone with a sensor.
 
21 - 28 of 28 Posts
Top