FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsHard
An accumulator precharge check is being performed on an aircraft with a hydraulic system operating pressure of 3,000 psi. According to typical maintenance practice, what nitrogen precharge pressure should the technician expect to find in the accumulator?
- AApproximately 1,000 psi, about one-third of system pressure
- BApproximately 100 psi, a nominal low pressure
- CApproximately 6,000 psi, twice system pressure
- DApproximately 3,000 psi, equal to system pressure
Show answer & explanationAnswer & explanation
Correct answer: A. Approximately 1,000 psi, about one-third of system pressure
Standard practice sets accumulator nitrogen precharge at roughly one-third of the system operating pressure. For a 3,000 psi system, that is approximately 1,000 psi (3,000 psi ÷ 3 = 1,000 psi), allowing the accumulator to store and release fluid efficiently.
Why the other options are wrong
- B. 100 psi is far too low to be effective for this system pressure.
- C. Precharge above system pressure would prevent fluid from entering.
- D. Equal precharge would leave no room for fluid storage.
Accumulator Precharge Ratio
Accumulators are typically precharged with nitrogen to about one-third of the hydraulic system's rated operating pressure.
- Precharge ≈ system pressure ÷ 3
- Too low precharge causes piston to bottom out
- Too high precharge reduces fluid storage capacity
Memory trick: Divide by three to find the nitrogen key.