Properties of LP
LP-gas is a petroleum product separated out of natural gas and crude oil in the refining process. LP in “LP-gas”
stands for “liquefied petroleum” and includes both propane and butane.
Both propane and butane may be available in the marketplace and, if given a choice for use in a
recreation vehicle, propane should be the choice. Propane has a much lower boiling point, which makes it better for
Recreational Vehicles, particularly in cold weather, since the propane must “boil” to create the vapor that is extracted
from the container for use by the appliances. Commercial butane will not boil when the outside temperature is 15°F
(-10°C) or lower. Therefore, the appliances will not work due to a lack of vapor pressure. Propane, on the other hand,
boils at –44°F (–42°C) and will continue to provide the vapor for fuel. Since butane is not commonly available, this
text will focus only on propane. The following table provides details on LP-gas properties.
Propane is a true gas and conforms to
Boyle's Law in that its pressure is related
to temperature when the volume is
constant, and the volume varies directly
with pressure when the temperature is
constant. In addition, LP-gas expands
as pressure is reduced, so it expands
in all directions (Pascal's Law), and any
air movement from heat, motion, fans,
wind, etc., will move LP-gas around in a
space. While LP-gas is heavier than air
and, in a perfectly still environment, will
settle to the bottom of a space, it will not
react like this in real-world conditions.
Instead, once propane is mixed with air,
the LP-gas will not separate from the air.
Propane is nearly odorless and colorless as extracted. It looks and acts similar to water except for its boiling point. Water boils at
+212°F (100°C) at sea level, and propane boils at –44°F (–42°C) at sea level.
The boiling of either liquid produces
a steam or vapor. The vapor produced by propane is a colorless, flammable gas. The higher the temperature above the boiling point the greater
the “steam” pressure. Propane gas is compressed 270 times to a liquid state for storage. Thus one US gallon makes 36.4 cubic feet of gas
vapor at sea level. Each cubic foot has 2500 BTU and uses about 25 parts of air to one part of gas to burn efficiently. Fortunately, propane
gas limits of combustibility are rather narrow. The gas-to-air ratio must be between 2.5% and 9.6% to ignite. It takes approximately
1,000°F (540°C) to ignite the mixture, and it can burn at up to 3,500°F (1,925°C) when properly mixed with oxygen.
(Click the image to view the instructional video in Windows Media Format)
An odorant, usually ethyl mercaptan, is added to propane just after its manufacture as a warning agent. This sulfur compound gives the gas the rotten egg, skunk oil odor. One or more pounds of mercaptan is added to 10,000 gallons of propane; this makes the propane smell in concentrations of one-fifth of the lower limit of combustibility as required by NFPA 58, The Liquefied Petroleum Code.Another important property of propane is the expansion of liquid as it is warmed. Propane's volume increases about 1-1/2% for every 10°F (5.5°C) it is warmed. Heat the propane 100°F (55°C), and the container liquid volume will increase 15%.
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LP Gas Stands For:
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