SkyDrill

Accumulator piston movement above preload

Aviation Mechanic Airframe (AMA) practice question 2 of 15 on Hydraulic and Pneumatic Systems. ACS element AM.II.F.K7 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA cylindrical accumulator is designed for a preload of 1,300 psi in a 3,000-psi system. At what system pressure does the accumulator piston start to move within the cylinder?

  1. A1,301 psi
  2. B1,300 psi
  3. C3,000 psi, the full system pressure
Show the answer and explanation

Correct answer: A. 1,301 psi

  • A — correct The pump must create a pressure greater than the 1,300 psi preload before fluid can move the piston, and at 1,301 psi the piston starts to move within the cylinder.
  • B — incorrect At exactly the preload value the air pressure still balances the fluid, so the piston remains bottomed; system pressure must exceed the preload.
  • C — incorrect At 3,000 psi the piston has already backed up to its normal operating position; that is the end of its travel, not the point where movement begins.

BACKGROUND

In operation, the compressed-air chamber of an accumulator is charged to a predetermined pressure somewhat lower than system operating pressure, and this initial charge is called the accumulator preload. With a 1,300 psi preload introduced while hydraulic system pressure is zero, the air moves the piston toward the opposite end until it bottoms. The hydraulic pump must then create a pressure within the system greater than 1,300 psi before the fluid can actuate the piston; at 1,301 psi the piston starts to move, compressing the air as it goes. At 2,000 psi it has backed up several inches, and at 3,000 psi it has reached its normal operating position with the air compressed into less than half the cylinder length.

STUDY TIP

Work the example numerically rather than memorizing it: the piston moves as soon as fluid pressure exceeds preload by any amount, and stored fluid is returned as pressure falls back toward preload.

KEY POINTS

  • Accumulator preload is charged lower than system operating pressure.
  • The piston begins to move as soon as fluid pressure exceeds preload, at 1,301 psi in the 1,300 psi example.
  • At full system pressure the piston has reached its normal operating position.

SOURCES

  • sources/ama-airframe/ch12.txt "Operation" (Accumulators)
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON HYDRAULIC AND PNEUMATIC SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.