Gas Appliances vs High Altitudes

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George Boley

Gas Appliances vs High Altitudes

Post by George Boley »

Recently Trisha posted a subject regarding her refrigerator malfunctioning at high altitudes. I will attempt to share my thoughts on the matter. These thoughts are supported by my remembering (I hope) my firefighting training and being an appliance serviceman for a number of years.

Any propane-fired appliance that I am aware of requires 11" of water column (pressure) to operate on, but before we explore that, we need to provide some basic data impacting propane.

1. Atmospheric pressure (at sea level) is 14.7 psi. Lower the higher we go.
2. 11" of water column equals slightly less than 1/2 psi.
3. At 70 degrees, propane provides 127 psi, when it boils off into a vapor. At say, 40 degrees, that pressure is reduced to 72 psi. At freezing, it is only 59 psi.
4. Liquid propane is clear like water, but weighs half as much (4.2 lbs. per gal), in it's vapor state it is heavier than air
5. Propane is odorless in it's natural state; the odor is put in to detect leaks.
6. LP tanks are only filled to 80% of capacity to allow space for the vapors.

Propane, a/k/a LP, is liquified in our tanks under high pressure. It boils off into a vapor gas to be used in our appliances. The working pressure is very low, just enough to push a column of water up 11 inches. A regulator at the tank maintains this pressure. Inside the regulator, an adjustable spring pushes against one side of a diaphragm; atmospheric pressure pushes against the other side. The spring tension is adjusted so 11" of water column pressure is sent to the appliance. Once it is adjusted, it works rather well, providing consistent pressure on stationary applications, but RVs travel and sometimes to high places where the atmospheric pressure is significantly reduced. There it exerts less pressure against the spring, moving the diaphragm. As an example, at Trisha's lofty 7500 foot mark, atmospheric pressure is only 5.5 psi, which really reduces the gas pressure that the regulator puts out. The burner orifice is fixed as is the air shutter, so in the end (thank God we are finally getting there), I think the mixture is just too lean to be ignited.

In the final anaylsis, I view the reason some RVs' LP systems work better at high altitudes than others may very well be at what altitude their regulator was set to produce 11" of water column. If we could easily reset these things, say at 7500 feet, I think everything would work fine.

The other variable that some of Trisha's responders shared, was they noticed the problem only during cooler temperatures. As the data above reflects, our LP tanks produce lowering primary pressures for each degree the temperature goes down, due in part to the gasing off (changing from a liquid to a vapor) process being slowed in the tank. With that, I conclude.

Please don't lose sight of the fact that I am an old yankee with little formal education, so it anyone thinks better, I sure would like to hear about it.
George B
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bcope01
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Post by bcope01 »

Good explanation, George - Thanks!
Barb & Bill
2004 Born Free 22' Built for Two (Sold)
no longer towing a 2008 Smart ForTwo

Escondido, CA
Dave&JanPotter

Re: Gas Appliances vs High Altitudes

Post by Dave&JanPotter »

George Boley wrote: As an example, at Trisha's lofty 7500 foot mark, atmospheric pressure is only 5.5 psi, which really reduces the gas pressure that the regulator puts out.
That was a great detailed explanation George however you had me scratching my head over the 5.5 psi figure. I had to get out my old handbooks to look this one up and that was a pleasant trip down memory lane for which I thank you. According to Marks Standard Handbook for Mechanical Engineers, you won't drop to 5.5 psi of atmospheric pressure until you get to about 25,000 feet in altitude. At 7500 feet of altitude, the atmospheric pressure should be about 11 psi. This difference seems picky however at 5.5 psi of atmospheric pressure a human would have great difficulty breathing ie pilots and airplane passengers generally use oxygen above 12,000 feet which is slightly over 9 psi of atmospheric pressure. Thanks for the chance to dust off my slide rule :lol:
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bcope01
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Joined: Wed Dec 07, 2005 6:55 pm

Post by bcope01 »

Chart showing atmospheric pressure at altitude:
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Pressure.jpg
Pressure.jpg (102.42 KiB) Viewed 8049 times
Barb & Bill
2004 Born Free 22' Built for Two (Sold)
no longer towing a 2008 Smart ForTwo

Escondido, CA
George Boley

Post by George Boley »

David,
You are exactly right, I was using a chart edited by Glover & Young and Published by Seuoia Publishing. On their chart, I was looking at 7500 METERS not feet. 6562' shows 11.53 psi and 8202' shows 10.83 psi so 7500' must be some where in between. Thanks for setting the record straight, thats what so great about this chat room. Hope to meet you at Iowa rallies. George B
Bill Ruh

Gas Appliances vs High Altitudes

Post by Bill Ruh »

Hi George,

I am not an expert here, but I thought that the thinner air and reduced oxygen was more a factor than the propane pressure. I recall norcold offering high-altitude kits in the past, some that increased the air flow to the burner and some that reduced the burner orifice size. But the norcold tech support person I talked to this week had no knowledge of this except on the 322/323, so perhaps my memory and explanation are not correct.
George Boley

Post by George Boley »

Bill,
I'm not an expert either, I was just trying to reason the problem out, you could be right. We don't seem to know if that high altitude burner orifice had a smaller or larger hole. If it is larger it would tend to support my hypophsis. I do know that the natural gas orifice is larger and I think it's normal presure is lower than LP. The club needs a top notch gas man to help us settle this question. Sure wish you were going to the Iowa rallies, I thought of you when I was setting up the technical discussion panel that I will be the moderator of. Cheers and thanks for your imput. George B
Bill Ruh

Post by Bill Ruh »

Hi George,

My (limited) understanding is that the high-altitude orifice is smaller.
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