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The tanks, sometimes referred to as pressure vessels, are commonly equipped with a service valve (or main liquid valve), a fixed maximum liquid level gauge (or “spit valve”), a float gauge, and a pressure relief valve. The service valve regulates the flow of the liquid propane to the heater. The fixed maximum liquid level gauge provides an indication that the tank is filled to its maximum design quantity, or 80 percent of the total capacity of the tank. The float gauge provides a reading of the remaining capacity of the tank in a percentage. The pressure relief valve allows for the release of propane from the tank should the tank exceed the maximum design pressure. A pressure relief valve normally releases at 375 pounds per square inch (psi). Figure 2-11 provides additional information on propane management.
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Figure 2-11. Propane primer. (Propane pressures at different temperatures are listed in Appendix A.)
Propane Primer
Propane is a liquefied petroleum gas. Propane is preferred over butane and other hydrocarbons in balloon design because propane has a lower boiling point (propane -44 °F, butane 32 °F), and, therefore, a consistently higher vapor pressure for a given temperature. Under ideal circumstances, a gallon of propane produces 91,600 BTU of heat.
In its gaseous form, propane is odorless. However, an odorant (a strong smelling chemical compound) is added to propane to indicate the leakage of even small quantities of gas. The odorant normally added to propane, ethyl mercaptan, loses its odor when burned. Tanks should never be stored in an enclosed area, or near a heater and/or a device with a pilot light. Propane vapor is heavier than air, and will collect in low areas. Concentrated propane vapor constitutes an explosive hazard.
There is a popular misconception that propane is always at -44 °F when stored. This is incorrect—the propane, in the tank, is the same temperature as the ambient air. Propane turns cold when vaporizing, due to heat exchange.
The combustion of propane yields carbon dioxide and water.
The balloonist should be aware of the large volume of combustible mixture that will result from the escape of a small amount of liquid propane. As a rough approximation, a given volume of liquid propane produces a combustible mixture 6,800 times the original liquid propane volume.
The propane cylinder raises the boiling point of propane by trapping the pressure built up by the vaporized propane. Any given temperature will produce a specific pressure within the propane cylinder. This balance between temperature and pressure is referred to as the point of equilibrium. As long as the propane cylinder is neither completely full nor completely empty of the liquefied fuel, and no foreign substance such as air is present, the pressure within the cylinder is dependent upon the prevailing temperature of the liquid, and not upon the amount of liquid propane within the cylinder. Therefore, maintaining a proper propane temperature is necessary to supply sufficient fuel pressure to the burner. The temperature-pressure point of equilibrium is only applicable to containers containing vapor over the liquid. While propane vapor is easily compressible, propane liquid is practically incompressible.
Butane-propane mixtures can be a problem. At certain times of the year in certain areas, butane will be mixed with propane to increase its boiling point. A butane-propane mixture will produce a more yellow, sooty flame, may tend to go out when the blast valve is pulled, and the pressure available for a given temperature will be less.
Burners commonly used in hot air balloons are vaporizer burners. A vaporizer burner combines a vaporizer with a burner into a single unit where burner heat is used to vaporize the liquid propane being fed into the burner. The vaporizer normally consists of a coil in direct contact with the burner flame. If there is no fuel flow through one of the coils during burner operation, the coil may be damaged as a result of overheating.
The heat output of a burner is one of the parameters that indicate how a given balloon will perform in flight. A long sustained burn will produce a lower rating that the same time increment broken up into short burns. The lower output for a sustained burn is due to the inertia of the fuel, the friction hindering fuel flow, and pressure decay due to the withdrawal of liquid propane from the cylinder.
Periodic inspections of the airborne heating system should include a visual inspection of the hoses and fittings, and a high pressure leak check with a test gauge adaptor.
Source: Saum, Nick. “Propane and Fuel Management.”
Joint publication of the Safety and Education Committees of the Balloon Federation of America, 1991.
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Figure 2-12. Balloon inflation using a typical inflation fan.Support Equipment
Standard support equipment for ballooning includes an inflation fan, transport/chase vehicle, and small miscellaneous items, such as igniters, drop lines, gloves, spare parts, and helmets. Inflation Fans
　
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