FUEL CROSS-FEED, FIREWALL SHUTOFF, AND TANK SELECTOR VALVES.

 Inspect these valves for leakage and proper operation as follows:

a.                           Internal leakage can be checked by placing the appropriate valve in the "off' posi­tion, draining the fuel strainer bowl, and ob­serving if fuel continues to flow into it. Check all valves located downstream of boost pumps with the pump(s) operating. Do not operate the pump(s) longer than necessary.

b.                           External leakage from these units can result in a severe fire hazard, especially if the unit is located under the cabin floor or within a similarly-confined area. Correct the cause of any fuel stains associated with fuel leakage.

c.                           Selector Handles. Check the operation of each handle or control to see that it indicates the actual position of the selector valve. To the placard location. Movement of the selector handle should be smooth and free of binding. Assure that stops and detents have positive ac­tion and smooth operational feel.  Worn or missing detents and stops can cause unreliable positioning of the fuel selector valve.

d.                           Worn Linkage. Inaccurate positioning of fuel selector valves can also be caused by worn mechanical linkage between the selector handle and the valve unit. An improper fuel valve position setting can seriously reduce engine power by restricting the available fuel flow. Check universal joints, pins, gears, splines, cams, levers, etc., for wear and exces­sive clearance which prevent the valve from positioning accurately or from obtaining fully "off' and "on" positions.

e.                           Assure that required placards are complete and legible. Replace those that are missing or cannot be read easily.

FUEL PUMPS. Inspect, repair, and overhaul boost pumps, emergency pumps, auxiliary pumps, and engine-driven pumps in accordance with the appropriate manufac­turer's instructions.

FUEL FILTERS, STRAINERS, AND DRAINS. Check each strainer and filter element for contamination. Determine and correct the source of any contaminants found. Replace throw-away filter elements with the recommended type. Examine fuel strainer bowls to see that they are properly installed according to the direction of the fuel flow. Check the operation of all drain devices to see that they operate properly and have positive shutoff action.

INDICATOR SYSTEMS. Inspect, service, and adjust the fuel indicator systems according to the manufacturer's instructions. Determine that the required placards and in­strument markings are complete and legible.

4.7.9 FUEL SYSTEM PRECAUTIONS. In servicing fuel systems, remember that fuel is flammable and that the danger of fire or ex­plosion always exists. The following precau­tions should be taken:

a.                           Aircraft being serviced or having the fuel system repaired must be properly grounded.

b.               Spilled fuel must be neutralized or re­moved as quickly as possible.

c.               Open fuel lines must be capped.

d.               Fire-extinguishing equipment must always be available.

e.                           Metal fuel tanks must not be welded or soldered unless they have been adequately purged of fuel fumes. Keeping a tank or cell filled with carbon dioxide will prevent explo­sion of fuel fumes.

f.                            Do not use Teflon tape on any fuel lines to avoid getting the tape between the flare and fitting, which can cause fluid leaks.