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Regulated pressure for a differential compression test

Aviation Mechanic Powerplant (AMP) practice question 11 of 13 on Reciprocating Engines. ACS element AM.III.A.K8 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONTo what value is the regulated pressure adjusted when reading cylinder pressure with a differential pressure tester?

  1. A40 psi
  2. B80 psi
  3. C100 psi
Show the answer and explanation

Correct answer: B. 80 psi

  • A — incorrect That is below the value the procedure specifies and would not produce a comparable reading.
  • B — correct The procedure calls for the regulated pressure to be adjusted to 80 psi before the cylinder pressure gauge reading is compared with the minimum specified for the engine.
  • C — incorrect That figure is the low end of the compressed air supply range connected to the tester, not the regulated test pressure.

BACKGROUND

The cylinder compression test determines whether the valves, piston rings, and pistons are adequately sealing the combustion chamber, and its purpose is to decide whether cylinder replacement is necessary. A differential pressure tester measures leakage through the cylinder, working on the principle that a given airflow through a fixed orifice produces a constant pressure drop. The tester assembly is connected to a 100 to 150 psi compressed air supply, and the test is made with the piston at top center of the compression stroke. With regulated pressure adjusted to 80 psi, a cylinder pressure reading below the minimum specified for that engine calls for further investigation.

STUDY TIP

Keep the two pressures separate in your mind: 100 to 150 psi is the shop air supply, while 80 psi is the regulated pressure applied to the cylinder.

KEY POINTS

  • The differential tester is fed from a 100 to 150 psi air supply.
  • Regulated pressure is set to 80 psi for the cylinder reading.
  • The piston must be at top center of the compression stroke.

SOURCES

  • FAA-H-8083-32B ch10 "Differential Pressure Tester"
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MORE ON RECIPROCATING ENGINES

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.