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Maximum acetylene regulator setting

Aviation Mechanic Airframe (AMA) practice question 19 of 20 on Metallic Structures. ACS element AM.II.A.K9 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONWhat is the highest pressure at which the acetylene pressure gauge should ever be set for welding or cutting?

  1. A15 psi
  2. B50 psi
  3. C29.4 psi
Show the answer and explanation

Correct answer: A. 15 psi

  • A — correct The handbook states that the acetylene pressure gauge should never be set higher than 15 psi for welding or cutting.
  • B — incorrect This is more than three times the stated limit and well past the pressure at which free acetylene becomes unstable.
  • C — incorrect This is the pressure at which pure acetylene in a free state explodes from a slight shock, not a working limit.

BACKGROUND

Acetylene is the primary fuel for oxy-fuel welding and cutting, and it is chemically very unstable. It is shipped in special cylinders packed with a porous material that is saturated with acetone; the acetylene dissolves in that solution and becomes stable. Pure acetylene stored in a free state explodes from a slight shock at 29.4 pounds per square inch, and for that reason the acetylene pressure gauge should never be set higher than 15 psi for welding or cutting. A soft or harsh flame is obtained by decreasing or increasing the working pressure of both gases, while still observing that maximum working pressure of 15 psi for acetylene. Oxygen, by contrast, is a colorless, odorless, nonflammable gas used to increase the combustion rate and so the flame temperature of the fuel gas.

STUDY TIP

Keep the two acetylene numbers distinct in your mind: 15 psi is the working ceiling, 29.4 psi is the explosion point for free acetylene.

KEY POINTS

  • The acetylene gauge is never set above 15 psi for welding or cutting.
  • Free acetylene explodes from a slight shock at 29.4 psi.
  • Cylinder acetylene is kept stable by dissolving it in acetone held in a porous filler.

SOURCES

  • sources/ama-airframe/ch05.txt "Welding Gases — Acetylene"
  • sources/ama-airframe/ch05.txt "Welding Gases — Oxygen"
  • sources/ama-airframe/ch05.txt "Soft or Harsh Flames"
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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.