When water is noted in fuel sumps, continue to drain fuel until water is no longer evident in
Fuel Strainers. Fuel strainers remove dirt, water, and other foreign particles from the fuel. They are usually
located in the fuel tank outlets or as part of the auxiliary pump assembly. They are also installed in carburetors and other
Types. Fuel tank, fuel sump, and carburetor/fuel metering strainers are the types explained below.
Various types are also shown in figure 2-6.
Fuel tank. Fuel tank strainers have a comparatively coarse mesh to prevent large particles from
entering the fuel system.
Fuel sump. Fuel sump strainers are located at a low point between the fuel tank and the engine-
driven pump. The mesh size is finer, usually being 40 or more mesh per inch.
Carburetor/fuel metering. Carburetors and other fuel-metering devices have screens or sintered
metal filters. These are usually designed to remove all particles larger than 40 microns.
Maintenance. Fuel strainer removal, inspection, cleaning, and replacement should be accomplished in
accordance with the applicable aircraft maintenance manual. General procedures are covered in the following
Removal. Remove strainer in accordance with aircraft maintenance manual making sure to place
the fuel selector valve in the off position prior to removal.
Inspection. Inspect strainer for dents, tears, clogging, foreign particles, and separation of solder
joints. Inspect body and cap for cracks or other damage. Replace strainer if punctured.
· Drycleaning solvent is flammable and solvent vapors are toxic. Use P-D-680, Type II
Solvent in a well-ventilated area. Keep away from open flames. Avoid prolonged solvent
contact with skin.
· When using air pressure, be extremely careful. Do not blow stream of air toward yourself or any
other person. Users of air pressure and personnel within the immediate area shall wear safety
glasses, goggles, or face shield. Ear protection may be required. Pressure will not exceed 30
psig. Failure to comply may result in injury.
Cleaning. Clean strainers with dry-cleaning solvent P-D-680, Type II. Blow dry with filtered, low
pressure, compressed air.
Replacement. Replace strainer in accordance with applicable aircraft maintenance manual.
Float Switches. Float switches are used to illuminate caution lights located on the cockpit instrument panel.
Illumination usually occurs when the fuel level falls below a certain point. A typical float switch unit is shown in figure 2-
7. Inspect switch for cracks, damage, corrosion, and security. Replace if damage exceeds inspection requirements in
the applicable maintenance manual.
Fuel Cells and Tanks. Fuel Cell and tank types, inspection, maintenance, purging, preservation handling,
storage, and depreservation are described in the following paragraphs.
Types. There are two basic fuel cell and tank types. These types are the fuel cell and the integral fuel
Integral. Integral tanks are compartments of the structure of an aircraft (as shown in figure 2-8)
designed to contain fuel. They are manufactured with a liquid-tight boundary, commonly called a seal plane, which has
been sealed with gaskets, structural adhesives, elastic films or other sealants. They have been built into both the wing
and fuselage sections of the aircraft with the primary structure forming the boundaries of the fuel tanks.