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Saturday, December 1, 2001

FOG - Steve Answers a Reader's Question

Since he lives in British Columbia, I invited one of my buddies, Steve Froese, to address this question from a fellow Canadian:

My propane generator will not run unless I heat the tank with a battery warmer. What can I do to fix this problem? Fred H., (Gold River, NS, Canada)

Fred, many people believe that “LP” stands for “Liquid Propane,” but it actually means “Liquefied Petroleum.” Consumer LP gasses include primarily propane, butane, and natural gas.

In Canada, the LP delivered by fuel providers is propane, but in many US states, LP is often a mixture of propane and butane, usually with much higher butane content. I mention this to introduce the issue of vaporization temperature. Propane has a boiling point of -40 degrees C., whereas butane has a boiling point of 0 degrees C. If the ambient temperature is below 0 degrees C., butane liquid does not boil, and therefore does not create vapor in the container. Similarly for propane below -40 degrees. Since most areas in Canada drop well below 0 degrees in the winter, or even in late fall, and some places drop below -40, vaporization is sometimes a problem, especially with butane. I’ll touch more on this issue later.

In terms of your problem, I will first assume that your generator is LP vapor fueled, as opposed to LP liquid. As per my comments above, if you have been traveling in the USA recently, your LP tank may be filled with a butane mixture. If so, this will increase your vaporization temperature. In addition, the more empty your LP container is, the more difficult it will be for vaporization to occur at lower temperatures. These two issues can be mitigated by completely filling your LP container at a fueling station in your area. This will ensure that you get propane into your container and maximize the energy capacity of the fuel.

Temperatures in your area are not likely near freezing, at least in the daytime, so I’m not sure your problem is directly related to ambient temperature. Other causes may include fuel delivery problems such as a dirty or frozen shut-off solenoid or regulator, low system pressure, dirty or mistuned carburetor, or even a system leak. It is important that you have your propane system professionally inspected annually to make sure it is safe and in good operating condition. 

Low system pressure and leaks reduce the fuel delivery capacity of the system. Although these problems would generally not be resolved by heating the tank, it is not impossible, since heating the container does increase the vaporization rate of the propane, and therefore improves the gas flow. Although it is probably not the case here, an undersized propane container, solenoid or tubing will also cause a problem if the total flow demand exceeds the system flow capacity. In such a case, the system will actually freeze-up while attempting to provide adequate flow. This is somewhat common when an LP generator is added to an existing propane system, increasing the total gas demand above the original design specifications.

To attempt to resolve your problem, have the propane container completely filled (to 80%), the propane system inspected, and the generator serviced. Also, remember that propane is flammable, so heating the container can be dangerous. It appears that you are doing it safely, but be sure not to use any method which can produce spark or flame. Hope this helps! Steve...

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