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Filtering capability of a micron fuel filter

Aviation Mechanic Powerplant (AMP) practice question 20 of 20 on Engine Fuel and Fuel Metering Systems. ACS element AM.III.I.K15 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONThe porous cellulose cartridge of a micron fuel filter is capable of removing foreign matter measuring

  1. A35 to 200 microns
  2. B10 to 25 microns
  3. C1 to 2 microns
Show the answer and explanation

Correct answer: B. 10 to 25 microns

  • A — incorrect Thirty-five and 200 are mesh numbers for the widely used screen-type filters, not the micron rating of the cellulose cartridge.
  • B — correct The handbook states that the cellulose material frequently used in micron filter cartridges removes foreign matter measuring from 10 to 25 microns.
  • C — incorrect This is finer than the rating given for the micron filter; the smallest particles it is credited with removing measure about 10 microns.

BACKGROUND

A low-pressure filter is installed between the supply tanks and the engine fuel system to protect the engine-driven pump and the control devices, and an additional high-pressure filter is installed between the pump and the fuel control. The three most common types are the micron filter, the wafer screen filter, and the plain screen mesh filter. The micron filter has the greatest filtering action of any present-day type and is rated in microns, a micron being one thousandth of one millimeter. Its porous cellulose cartridge removes foreign matter measuring from 10 to 25 microns, and the minute openings make it susceptible to clogging, so a bypass valve is a necessary safety factor. The cellulose material also absorbs water, which is why periodic servicing and element replacement are imperative.

STUDY TIP

Keep micron ratings and mesh numbers in separate mental boxes, because the 200-mesh and 35-mesh screens are often confused with micron figures. Remember why the bypass valve exists: the finer the filter, the more likely it is to clog.

KEY POINTS

  • Micron filters have the greatest filtering action and are rated in microns.
  • The cellulose cartridge removes foreign matter from 10 to 25 microns.
  • Because it clogs easily, a bypass valve is a necessary safety feature.

SOURCES

  • amp-powerplant/ch02.txt "Fuel Filters"
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MORE ON ENGINE FUEL AND FUEL METERING SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.