vertical or horizontal, and contain 10, 15, or 18 gallons of  propane. Larger tanks are available for larger ride balloons.  [Figure 2-10] helps with balloon landings and cushions some of the  impact force at landing. The basket contains the fuel tanks,  instruments, pilot, and passengers.  Aluminum, stainless steel, or flexible nylon poles (in  conjunction with stainless steel cables) located on the upper  portion of the structure transfer the basket load to the envelope  attachment points and support the burner assembly. Quick  pins or aircraft bolts connect the support tubes, with nylon  rods usually inserted into the sockets, and the cables attached  around them. Lower frame tubes support the floor, permitting  the floor load to be transferred to the lower frames. Oak  skids, usually affixed to the floor, add rigidity and provide a  point of abrasive resistance to the floor. Rattan sidewalls of  varying thickness, design, and color surround and protect the  passengers, equipment, and fuel tanks. Larger baskets, usually  found on large ride balloons, may have padded basket dividers  to form passenger compartments. 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. As required by 14 CFR part 31, balloons are equipped with  an altimeter, a rate of climb indicator, fuel quantity gauges,  and an envelope temperature gauge. Many newer balloons use  some type of electronic instrument system, but older balloons  may still be equipped with traditional, pressure driven analog  instruments. The most common arrangement of instruments is a small  pod or package which includes the altimeter, rate of climb  indicator (variometer or vertical speed indicator), and the  envelope temperature gauge (pyrometer). A cable is plugged  into the instrument package during the preflight or layout  process which connects to a sensor located in the top of the  balloon and operates the envelope temperature gauge. Fuel  quantity gauges, located on the top portion of each fuel tank,  provide a reference for the quantity of fuel remaining in the  tank. As these gauges are mechanical, they are sometimes  inaccurate, and in most configurations do not read from 0 to  100 percent. This needs to be taken into consideration during  the flight planning process.  In recent years, many manufacturers have added a wireless  system that transmits the temperature signal to a receiver in  the basket via a radio or infrared signal. This eliminates the  necessity of a wire being located in the balloon envelope.  These instrument systems are popular, but have reliability  issues because radio interference or the thermal “plume” from  the burner can degrade the signal transmission.  Balloons generate heat through the use of propane. The  propane is contained in aluminum or stainless steel tanks  mounted inside the basket. These tanks may be either  Figure 2-10.  Typical fuel tank. 2-7 MAIN LIQUID VALVE FUEL QUANTITY GAUGE LIQUID LEVEL VALVE LIQUID LEVEL PICK-UP LIQUID PICK-UP (DIP TUBE) QUANTITY FLOAT 6 5 4 3 2 1 1 6 2 3 5 4 TYPICAL FUEL TANK (VERTICAL) Fuel Tanks Instruments