Gas Appliances vs High Altitudes
Posted: Mon May 15, 2006 10:06 am
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
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