FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsHard
A pneumatic emergency landing gear extension system uses a compressed air storage bottle with a volume of 250 cubic inches charged to 3,000 psi. When discharged, this air fills the gear actuating system lines and cylinders, which have a total volume of 750 cubic inches. Assuming no temperature change, what is the resulting pressure in the system after discharge?
- A2,250 psi
- B3,000 psi
- C1,500 psi
- D1,000 psi
Show answer & explanationAnswer & explanation
Correct answer: D. 1,000 psi
Using Boyle's Law, P1V1 = P2V2: (3,000 psi)(250 in³) = P2(750 in³). Solving, P2 = 750,000 ÷ 750 = 1,000 psi. As the gas expands into a larger total volume at constant temperature, its pressure drops proportionally.
Why the other options are wrong
- A. This does not match the Boyle's Law calculation using the given volumes.
- B. This ignores the expansion of gas into a larger volume.
- C. This is not the result of dividing 750,000 by 750.
Boyle's Law in Pneumatic Systems
At constant temperature, the pressure of a gas is inversely proportional to its volume: P1V1 = P2V2.
- Used to calculate final pressure when air bottle discharges into larger volume
- Applies to emergency pneumatic gear extension and other compressed air systems
- Assumes constant temperature (isothermal process)
Memory trick: Bigger space, same gas, lower pressure — squeeze law reversed.