You probably give your balloon’s fuel system little attention unless it develops a noticeable problem, such as a fuel leak. Many pilots bring a balloon system in for an annual inspection, and request that the cylinders not be opened. Frequently the balloon system is new or nearly new, and they expect no problems.
Some manufacturers do not require fuel cylinders to be opened as part of their checklists. They do require visual inspection of the exterior, and checks for leaking valves. Some manufacturers recommend the addition of methanol to the fuel. With an opened tank, methanol is easily added. Otherwise, it must be forced into the cylinder during refueling. You can fill a refueling adapter hose with methanol before hooking up to the propane supply hose, and the methanol will go into the cylinder with the propane. Do this annually for each cylinder.
We have routinely opened cylinders for annual inspections, and have found several problems we could not otherwise have found. We often find dead insects in the bottom of a cylinder. House flies are attracted to the smell of the odorizing agent in the propane, and crawl into the refueling fitting at the propane dealer’s tank. They are then blown into the cylinder with the propane the next time you refuel. Other dirt and debris may also be blown into your cylinder during refueling.
We have frequently found metal shavings inside new cylinders. The shavings had been left in the threads in the openings, and were dislodged when the valves were installed. We also found metal shavings inside cylinders of several balloons returning from a particular rally. One of the systems had pilot light regulator failures from the shavings. Another had a metal shaving lodged under the blast valve seat. Those two balloons did not fly the second day of the rally. After we found the shavings, some other pilots returning from the same rally brought their systems in to be checked for shavings. We removed them, and they had no more problems.
The fuel gauge float sometimes interferes with the fuel dip tube. If your fuel gauge indicates you still have fuel when the cylinder is empty, the float arm may need to be adjusted.
Many fuel system components must be serviced or replaced according to time limits imposed by the balloon manufacturer, the component manufacturer, the FAA, the Department of Transportation, or your balloon insurance carrier.
The US Department of Transportation requires that any propane cylinder to be transported within the US be inspected if it was manufactured more than 12 years ago. The manufacture date is stamped on the cylinder ring or a manufacturer’s data plate. It is illegal to fill and transport a cylinder unless it has a current inspection stamp. The cylinder can be visually inspected, and can be used for another 5 years from the date of the inspection stamp (the letter "E" with a month and year), or 10 years from the date of a hydrostatic test. The visual inspection is less expensive than the hydrostatic test, so most balloon fuel cylinders are visually inspected and recertified by a propane dealer licensed to perform the certification.
The pressure relief valve on the cylinder now has an expiration date 10 years from its date of manufacture. If you have a 12 year old cylinder, the pressure relief valve should have been replaced 2 years ago. Aerostar found that some of the pressure relief valves they inspected have failed in 5 to 7 years of service, and recommends their replacement every 5 years. I replaced 7 year old valves and found that half of them had bent stems, which could possibly cause them to stick open if they were ever popped open. Replace the pressure relief valves whenever the cylinders need to be recertified, or if they are over 5 years old.
Many balloon manufacturers and insurance companies require replacement of fuel hoses if they are more than 9 or 10 years old at the time of the annual inspection. If your hoses are in this age range, and your annual or 100 hour inspection is due shortly, you may want to have your repair station order the proper replacements.
Hoses may need replacement sooner, if they have been improperly stored, or if their covers have been nicked or abraded. Steel reinforced hoses should be replaced if they show signs of rust or corrosion from the reinforcing braid.
One item frequently overlooked is the 80 percent valve, or "spit valve." If a cylinder is more than 5 years old, you should inspect the spit valve stem and seal. When you empty a cylinder, remove the stem from the spit valve by unscrewing it all the way. Inspect the black rubber seal on the bottom of the stem. It should be shiny and flexible, with no cracks around its edge. If it is hard, has cracks around its edge, or a deep round groove in it, you should replace it. If it fails, your cylinder will be leaking propane, and you will be grounded. Carry a spare-they cost around a dollar. If your spit valve develops a leak, you can quickly replace its stem once the valve has finished spewing liquid propane. I would recommend replacing it while the cylinder has been drained for the annual inspection.
While refueling, the liquid propane spewing from the 80 percent valve chills the seal and causes it to harden. After it warms up and becomes soft, it may leak. To prevent leaking, turn the valve stem another 1/4 turn closed after allowing it to warm up.
Finally, when your annual inspection comes due, prepare for the repair station to service your fuel system. Bring it into the shop with as little fuel in it as possible. It saves the repair station time, and it saves you money.