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Car Forum / Driving, Maintenance, Tuning / RVs / August 2006Propane - temperature and altitude
Just returned last night from our annual pilgrimage to Yosemite, specifically Tuolumne Meadows. Awesome trip as usual. Normally I fill a 20 lb propane bottle before we leave and use it for a little propane stove usage, some heater, and a week of chilling the 3-way fridge. I then take the bottle off the camper and use it with the BBQ for the rest of the year, eg: I usually have plenty of LP for that week. Last year I ran out of propane. I am thinking it was a bad fill, but to be safe I carried two bottles this year and attached a flow meter with green/yellow/red markings indicating the pressure. As expected when we left from sea level with the temperature in the 70's, the pressur was in the "green". Our first night was at 6800 feet elevation, and the evening cooled to around 40 degrees fahrenheit. In the morning, the needle was in the low green, but by 9am in was in the middle zone. The increased elevation and the lower temperatures reduced the pressure of the liquid propane in the tank - some basic science. Throughout the week I saw the reflected. During the day at 8,600 feet elevation the needle was in the green, but each early morning (between 5am and 7am it was the coldest) the temp was 30-34 degrees and the needle would drop into the yellow zone. I got home last night and even though it was cooling off to low 60's, that and the sea-level but the guage back into the green zone - well above midway. I seem to recall I had the bottle last year filled on a particularly warm day. I think the warmer ambient temp combined with the sea-level air pressure led to a poor fill, so when we climbed above 8000 feet the tank did not perform. So it would appear for the best fill, I should take the tank to a fill station at the higher elevation earlier in the morning and have it filled there. But then what danger is there when the tank warms up and/or is moved down to sea level? I have read around and not found anything discussing this - other than mentioning that propane in general performs less efficiently at higher altitudes. > Just returned last night from our annual pilgrimage to Yosemite, > specifically Tuolumne Meadows. Awesome trip as usual. [quoted text clipped - 41 lines] > mentioning that propane in general performs less efficiently at higher > altitudes. Increased elevation...lower ambient air pressure makes for 'higher' relative pressure inside the bottle...right? My guess would the temperature differential. You might try 'purging' the tank. john > Our first night was at 6800 feet elevation, and the evening cooled to > around 40 degrees fahrenheit. In the morning, the needle was in the low > green, but by 9am in was in the middle zone. The increased elevation and > the lower temperatures reduced the pressure of the liquid propane in the > tank - some basic science. A pressure gauge on a propane tank is a useless piece of junk. There is no way an increase in elevation can reduce the pressure in a propane tank. > Throughout the week I saw the reflected. During the day at 8,600 feet > elevation the needle was in the green, but each early morning (between > 5am and 7am it was the coldest) the temp was 30-34 degrees and the needle > would drop into the yellow zone. That's because a pressure gauge on a propane tank is a useless piece of junk. Propane powered devices have pressure regulators because the pressure in the tank can vary widely (and the device does not need the high pressures that exist in the tank). > I seem to recall I had the bottle last year filled on a particularly warm > day. I think the warmer ambient temp combined with the sea-level air > pressure led to a poor fill, so when we climbed above 8000 feet the tank > did not perform. There are several ways a reatiler can determine your tank is full. None of them are based on pressure in the tank. On the other hand, a leak could cause a tank to "not perform." I have had this happen. See below. > So it would appear for the best fill, I should take the tank to a fill > station at the higher elevation earlier in the morning and have it filled > there. How about making sure the valve is closed properly. One other thing to check. On the valve assembly is a small valve that some retailers used to use to check for a full tank. It opens with a screwdriver, and the dealer would fill until liquid propane came out of that valve, then stop filling and close the valve. On two occasions, I have found empty tanks that had that valve *slightly* open. Over a period of days or weeks, the propane leaked out. > But then what danger is there when the tank warms up and/or is moved down > to sea level? None whatsoever. If there was a hazard related to altitude, it would be from bringing a full tank from sea level to high altitude, not the other way around. > I have read around and not found anything discussing this - other than > mentioning that propane in general performs less efficiently at higher > altitudes. That's because the only real issue is that you have allowed the pressure gauge to lead you astray. It's junk. Get rid of it. Austin >> Our first night was at 6800 feet elevation, and the evening cooled to >> around 40 degrees fahrenheit. In the morning, the needle was in the [quoted text clipped - 6 lines] > There is no way an increase in elevation can reduce the pressure in a > propane tank. Thanks for the comments. It is actually a flow-meter, not a pressure guage (as the pressure should be nearly constant untli the tank is virtually empty). However, I was trying to keep things simplified. Do you have a suggestion on how to more effectively use a tank of propane at high altitude in cold climates? >>> Our first night was at 6800 feet elevation, and the evening cooled to >>> around 40 degrees fahrenheit. In the morning, the needle was in the [quoted text clipped - 13 lines] > Do you have a suggestion on how to more effectively use a tank of propane > at high altitude in cold climates? Steph, Austin is right that air pressure has no effect on the pressure inside the tank. The elevation has nothing to do with how much material is in the tank. This is what all that metal that the tank is made out of is for. When they fill up a tank (at least in the 3 places that I fill up) they do it by weight, not by pressure. I purchase pounds of gas. They put the cylinder onto a scale and load in the prescribed amount of pounds of material. Then they stop it. Now, when the gas is being used, the internal pressure will decrease as the gas is being used - the whole time, not just at the end of the bottle. The gas regulator makes it so that the output pressure (what is in the line at the stove) is a constant pressure, as prescribed by your camper manufacturer. The flow meter that you have is in the line after the regulator, and is just seeing how much gas is going by the meter at that point in the line. It is not measuring how much is left in the tank. So, what you have is a stable delivery system. What varies here is how the gas is being consumed by the appliances. At different altitudes/ambient temperatures the gas will be used at different rates, and this is what I believe you are really seeing. It's a usage thing, not a tank thing. You will use more when it is cold (more heating is needed), and you will see different readings on the flow meter. My advice on 'how to more effectively use a tank of propane at high altitude in cold climates' would be to plan on more usage in those environments to get the same results. Your move to have a second tank along is the answer. Hope this helps, Tomes >>>> Our first night was at 6800 feet elevation, and the evening cooled to >>>> around 40 degrees fahrenheit. In the morning, the needle was in the [quoted text clipped - 42 lines] > Hope this helps, > Tomes Propane tanks will be almost contant pressure until empty. As long as there is liquid propane in the tank, the pressure does not change. Is why a pressure guage fails to tell you how much gas is remaining. You could get a difference in pressure past the regulator, depending where the reference for the guage is. If it is a differential to ambient air pressure, it will change, if it is based on a spring and absolute pressure, the pressure should not change. As you say, in cold weather, you burn more gas to heat things. The pressure inside the tank fluctuates with tank temperature. Otherwise nothing else should affect the run time of a tank. > Propane tanks will be almost contant pressure until empty. As long as there > is liquid propane in the tank, the pressure does not change. Is why a [quoted text clipped - 4 lines] > should not change. As you say, in cold weather, you burn more gas to heat > things. > Steph, Austin is right that air pressure has no effect on the pressure > inside the tank. The elevation has nothing to do with how much material > is > in the tank. I agree that the amount (weight) of the gas in the bottle will not change, but the pressure indeed will with a change in ambient temperature or pressure. Temperature will change the absolute pressure, though elevation (pressure) will only change the relative pressure (difference between tank and ambient pressure). In either case, the regulator will handle it, one of the reasons it is there. > This is what all that metal that the tank is made out of is > for. When they fill up a tank (at least in the 3 places that I fill up) > they do it by weight, not by pressure. I purchase pounds of gas. I have purchased both pounds and "gallons", though when buying "gallons", they convert it from pounds. There will be more gallons per pound at a lower temperature. Ambient pressure will have a negligible effect, if any at all.  SignatureKarl & Angela `02 Durango `05 Fleetwood Allegiance >> Steph, Austin is right that air pressure has no effect on the pressure >> inside the tank. The elevation has nothing to do with how much material [quoted text clipped - 16 lines] > lower temperature. Ambient pressure will have a negligible effect, if any > at all. Temperature will also have a negligible effect on gallons relative to pounds. In the liquid state the size change with temperature will be "tiny" (Propane weight: 4.24 pounds of per gallon at 60F). Pressure changes a lot. At 40 F the pressure is 63 PSI and at 80F it is 129 PSI and at 100F it is 174 PSI Due to the pressure change there is a limit as to how much propane can be drawn at a time. As the propane is used the temperature of the liquid drops, thereby limiting the amount vaporized (at -44F it will not vaporize). But that should never be a problem for RV use. >> I agree that the amount (weight) of the gas in the bottle will not >> change, but the pressure indeed will with a change in ambient temperature [quoted text clipped - 17 lines] > pounds. In the liquid state the size change with temperature will be > "tiny" (Propane weight: 4.24 pounds of per gallon at 60F). 4.24 lbs/gallon at 60F, any idea what it is at 90F, 30F? According to a propane FAQ (Tevis Oil) a 10F change in ambient temperature will have approximately 1.5% change in volume. I guess it depends on what you think "negligible" is. The gallon is a measure of volume, 231 cubic inches IIRC. At a lower temperature, a gallon will weigh more than at a higher temperature because it's density will be higher when cooler. > Pressure changes a lot. At 40 F the pressure is 63 PSI and at 80F it is > 129 PSI and at 100F it is 174 PSI Which does not change the amount of propane that is there, only it's state. Also you are talking about temperature here, I was talking about ambient pressure vs tank pressure and it's effect on the number of pounds per gallon. > Due to the pressure change there is a limit as to how much propane can > be drawn at a time. As the propane is used the temperature of the > liquid drops, thereby limiting the amount vaporized (at -44F it will not > vaporize). But that should never be a problem for RV use. I would have to agree that the vast majority of people will not be using their RV's at -44 and thus that is a non-issue, but as to there being a limit as to how much propane can be drawn (which in the above you seem to say is a function of temperature effects on pressure) it would depend on what unit of measure is being used. SignatureKarl & Angela `02 Durango `05 Fleetwood Allegiance >>> I agree that the amount (weight) of the gas in the bottle will not >>> change, but the pressure indeed will with a change in ambient temperature [quoted text clipped - 44 lines] > say is a function of temperature effects on pressure) it would depend on > what unit of measure is being used. What I mean is that for a given size tank there is a limit on how much propane can be vaporized in a given period of time. The propane cools as it evaporates reducing the amount that can be vaporized. As the outside temperature drops this reduces it even further. For this reason people that heat their houses with propane can run into reduced flow even when the temperature is still well above the -44F. The Ideal Gas formula is: PV=nRT P=Pressure V=Volume n=number of moles of gas R=Universal gas constant T=Temperature Therefore, in a confined space (closed propane tank), the Volume is constant, the number of moles of gas is constant, and R is by definition a constant, SO, as the temperature rises, the pressure rises, and as the temperature falls, the pressure falls. However, most of the propane in the tank is in *liquid* form, under high pressure, The Ideal Gas formula really only applies to gas. How much of liquid propane becomes a gas (vaporizes) is related mostly to temperature. Propane becomes a gas at something like -44 degrees at sea level pressure. It exists as mostly a liquid in the tank because of the high pressure it is under. As you use up the gas in your stove, more of the liquid propane vaporizes within the tank. Eventually, almost of the liquid propane vaporizes and the tank becomes mostly empty. Tanks are built to withstand high pressures. Filling the tank correctly (by weight, not by volume) should not give a significantly different result at high or low altitudes or temperatures. At high altitudes, gas (outside of the pressurized tank) behaves differently - with the lower atmospheric pressure, it comes out of the nozzle 'faster'. In fact, some propane lanterns have a "high pressure nozzle" one can use, which has a SMALLER orifice than the regular nozzle, since one the propane is coming out of the regular nozzle at a faster rate at high altitudes, due to lower ambient pressure. For stoves, I do not believe there is a different nozzle available, because one can adjust the flame anyway by hand. Therefore, most people do not notice the difference in the gas flame on a stove at different altitudes. I would guess that last year you had a 'bad fill' of your tank. > Just returned last night from our annual pilgrimage to Yosemite, > specifically Tuolumne Meadows. Awesome trip as usual. [quoted text clipped - 41 lines] > mentioning that propane in general performs less efficiently at higher > altitudes. |
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