features, such as the tank vents, sump drain, filler spout, etc.  When a bladder tank develops a leak, the technician can patch  it following manufacturer’s instructions. The cell can also be  removed and sent to a fuel tank repair station familiar with  and equipped to perform such repairs. The soft flexible nature of bladder fuel tanks requires that they  remain wet. Should it become necessary to store a bladder  tank without fuel in it for an extended period of time, it is  common to wipe the inside of the tank with a coating of clean  engine oil. Follow the manufacturer’s instructions for the dry  storage procedures for fuel cells.  On many aircraft, especially transport category and high- performance aircraft, part of the structure of the wings or  fuselage is sealed with a fuel resistant two-part sealant to form  a fuel tank. The sealed skin and structural members provide  the highest volume of space available with the lowest weight.  This type of tank is called an integral fuel tank since it forms  a tank as a unit within the airframe structure. Integral fuel tanks in the otherwise unused space inside the  wings are most common. Aircraft with integral fuel tanks in  the wings are said to have wet wings. For fuel management  purposes, sometimes a wing is sealed into separate tanks  and may include a surge tank or an overflow tank, which is  normally empty but sealed to hold fuel when needed.  When an aircraft maneuvers, the long horizontal nature of  an integral wing tank requires baffling to keep the fuel from  sloshing. The wing ribs and box beam structural members  serve as baffles and others may be added specifically for  that purpose. Baffle check valves are commonly used. These  valves allow fuel to move to the low, inboard sections of the  tank but prevent it from moving outboard. They ensure that  the fuel boost pumps located in the bottom of the tanks at  the lowest points above the sumps always have fuel to pump  regardless of aircraft attitude.  [Figure 14-32] Integral fuel tanks must have access panels for inspection  and repairs of the tanks and other fuel system components.  On large aircraft, technicians physically enter the tank for  maintenance. Transport category aircraft often have more  than a dozen oval access panels or tank plates on the bottom  surface of the wing for this purpose.  [Figure 14-33A]  These  aluminum panels are each sealed into place with an O-ring  and an aluminum gasket for electrostatic bonding. An outer  clamp ring is tightened to the inner panel with screws, as  shown in  Figure 14-33B. When entering and performing maintenance on an integral  fuel tank, all fuel must be emptied from the tank and strict  Flexible fuel hose has a synthetic rubber interior with a  reinforcing fiber braid wrap covered by a synthetic exterior.  Aircraft fuel lines can be rigid or flexible depending on location  and application. Rigid lines are often made of aluminum alloy  and are connected with Army/Navy (AN) or military standard  (MS) fittings. However, in the engine compartment, wheel  wells, and other areas, subject to damage from debris, abrasion,  and heat, stainless steel lines are often used.  Aircraft using integral fuel tanks normally have sophisticated  fuel systems that include in-tank boost pumps. There are  usually at least two pumps in each tank that deliver fuel to  the engine(s) under positive pressure. On various aircraft,  these in-tank boost pumps are also used to transfer fuel to  other tanks, jettison fuel, and defuel the aircraft.  safety procedures must be followed. Fuel vapors must be  purged from the tank and respiratory equipment must be used  by the technician. A full-time spotter must be positioned just  outside of the tank to assist if needed. Fuel Lines and Fittings 14-22 Integral Fuel Tanks Figure 14-32.  Baffle check valves are installed in the locations  shown in the integral tank rib structure of a Boeing 737 airliner.  Fuel is prevented from flowing outboard during maneuvers. The  tank boost pumps are located inboard of WBL 157. INBOARD Surge tank 5 valves (WBL 157.0) 6 valves (WBL 227.0) 1 valve (WBL 557.0) Body Valve