Bleeding off propane before high elevations

[DXSMac]

I have noticed propane expands at higher elevations. The guage reads "more" at higher elevations. So, if you fill a propane tank at lower elevation, knowing you are going to higher elevation (6,000 feet or more), should you "bleed off" the propane somehow, by staying somewhere and using everything on propane?

I'm kind of following that. Or is this one of passionate 50/50 things, arguments for and arguments against don't cancel each other out? (Like wheel covers on wheels......)

[bakken]

No need to worry, as the pressure change is not that great.

[Herk7769]

The new tanks have over fill prevention devices and if filled correctly you will never over pressure them.

Propane OPD - Overfill Prevention Device Cylinder Valves

[OldCoot]

Atmospheric pressure decreases as altitude increases. Air Pressure and Altitude above Sea Level

[Herk7769]

Originally Posted by OldCoot

Atmospheric pressure decreases as altitude increases. Air Pressure and Altitude above Sea Level

This is, of course, true. However the tank is a closed system. It only responds to temperature variations and not pressure fluctuations.

While it is also true that ambient temperature decreases as you rise in altitude, (2.5 - 4 degrees cooler per 1,000 feet of pressure altitude - Does The Temperature Drop As You Increase Altitude? | F.A.Q. | Seattle News, Weather, Sports, Breaking News | KOMO News), the OFPD ensures there is sufficient expansion space. If the OFPD is defeated, you could over pressurize the tank but not by going UP. You would have to go down where it is "hotter" to increase pressure inside the tank.

Get the tank hot enough and the tank's pressure will drop to zero when it explodes.

[gasman6674]

If the tank is properly filled to the 80% level there is plenty of room for expansion. OPD (overfill protection device) valves that are required on all 20# thru 40# cylinders and all permanent vapor RV tanks will not allow the tank to be filled past 80% usually they trip well before that level. Of course they are mechanical and can fail so if you suspect it weight the tank. Take the tare weight of the cylinder that is stamped on the collar (ex TW 18 ) and deduct from the total weight EX total wt 38# - 18#tw = 20# gas.
FYI Propane weighs 4.24 pounds per gallon so a full 20# cylinder will hold approx. 5 gallons

[DXSMac]

Well, I had a tank filled to 80% once, then when I went to a higher elevation, the needle shot WAY PAST THE FULL mark. I was concerned!

[RPAspey]

if your gauge uses PRESSURE to measure how full the tank is, then the change in elevation WILL cause an errant reading. The gauge measures tank pressure relative to atmospheric pressure. Generally a cheap gauge will only be reasonably accurate if you are at the same elevation as the factory. At lower elevations, the gauge would read lower due to higher air pressure. Of course if you are higher in elevation, the gauge would read higher due to lower air pressure.

If you have a float type level gauge, then altitude would not make a difference. I don't think campers would have this kind due to DOT regulations.

[w4drr]

A pressure gauge is meaningless with regard to how much propane is in the tank. The propane is a liquid, and the pressure in the tank will remain constant, give or take due to temperature, until all the liquid propane is gone. The only true measure of how much propane is in the tank is the weight, which was previously mentioned. The only real purpose of a propane pressure gauge is to enrich those who make and sell them.

Bob

[gasman6674]

RPAspey
There are not any rules that I am aware of that prohibit a float gauge in a cylinder. Manchester and Worhington both offer a tank with a gauge. You can also retrofit existing 20 and 30# tanks with a new OPD gauge valve so you can have an accurate level indication.

[w4drr]

They also make those stick-on magnet "level guages" that work based on the fact the liquid propane will be at a different temperature than the gaseous propane above it. I never had much luck with them. The way I test my tanks is lightly tap on them and listen to the sound. I always manually switch the valve between tanks, so one is always full while the other is in use. The full tank is the reference. You can train your ear to the sound and get a pretty good idea how much liquid is left in the tank.

Bob

[OldCoot]

Originally Posted by DXSMac

Well, I had a tank filled to 80% once, then when I went to a higher elevation, the needle shot WAY PAST THE FULL mark. I was concerned!

As Herk stated in post 5, the propane tank is a closed system and is not influenced by altitude, just heat.

[RPAspey]

Originally Posted by gasman6674

RPAspey
There are not any rules that I am aware of that prohibit a float gauge in a cylinder. Manchester and Worhington both offer a tank with a gauge. You can also retrofit existing 20 and 30# tanks with a new OPD gauge valve so you can have an accurate level indication.

Ive never seen a valve with a float gauge. I'd like that. I remove my tanks and weigh them before every trip. My back ain't what it used to be!