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Hose material compatible with phosphate ester hydraulic fluid

Aviation Mechanic General (AMG) practice question 3 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.K3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic must select a synthetic rubber hose for a hydraulic system that uses phosphate ester base hydraulic fluid. Which hose material does the handbook describe as excellent for this fluid?

  1. AButyl
  2. BBuna-N
  3. CNeoprene, because of its abrasion resistance
Show the answer and explanation

Correct answer: A. Butyl

  • A — correct Butyl is described as an excellent material for use with phosphate ester base hydraulic fluid, though it must not be used with petroleum products.
  • B — incorrect Buna-N has excellent resistance to petroleum products, but the handbook says not to use it for phosphate ester base hydraulic fluid.
  • C — incorrect Neoprene has better abrasion resistance than Buna-N, but it also must not be used for phosphate ester base hydraulic fluid.

BACKGROUND

Pure rubber is never used in flexible fluid lines; synthetics such as Buna-N, neoprene, butyl, ethylene propylene diene rubber (EPDM) and Teflon are used instead. Buna-N has excellent resistance to petroleum products but must not be used with phosphate ester base hydraulic fluid. Neoprene, an acetylene-based synthetic, resists petroleum less well than Buna-N but has better abrasion resistance, and it also must not be used with phosphate ester fluid. Butyl, made from petroleum raw materials, is excellent with phosphate ester base hydraulic fluid but must not be used with petroleum products. Hose suitable for phosphate ester fluid carries a marking to that effect, and the applicable aircraft maintenance or parts manual should always be consulted for hose selection.

STUDY TIP

Pair each synthetic with its fluid: Buna-N and neoprene for petroleum, butyl for phosphate ester; the two families are not interchangeable.

KEY POINTS

  • Butyl is excellent with phosphate ester base hydraulic fluid but not with petroleum products.
  • Buna-N and neoprene resist petroleum products but must not be used with phosphate ester fluid.
  • Always confirm hose selection in the aircraft maintenance or parts manual.

SOURCES

  • FAA-H-8083-30B ch09 "Hose Materials & Construction" (Buna-N, Neoprene, Butyl)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.