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Selector valve arrangement in an open center system

Aviation Mechanic Airframe (AMA) practice question 7 of 15 on Hydraulic and Pneumatic Systems. ACS element AM.II.F.K2 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONIn an open center hydraulic system, the selector valves are always connected to each other how?

  1. AIn parallel
  2. BIn parallel through a pressure regulator
  3. CIn series
Show the answer and explanation

Correct answer: C. In series

  • A — incorrect Parallel arrangement of the directional control valves is the distinguishing feature of the closed-center system, not the open center system.
  • B — incorrect A pressure regulator is used with a constant delivery pump in a closed-center system; it does not describe how open center selector valves are connected.
  • C — correct In the open center system the selector valves are always connected in series with each other, so the system pressure line goes through each selector valve.

BACKGROUND

An open center system is one having fluid flow, but no pressure in the system when the actuating mechanisms are idle. The pump circulates the fluid from the reservoir, through the selector valves, and back to the reservoir. The open center system may employ any number of subsystems, with a selector valve for each subsystem, and those selector valves are always connected in series so the pressure line passes through each one. Fluid is allowed free passage through each selector valve back to the reservoir until one valve is positioned to operate a mechanism, at which point flow through the valve to the reservoir is blocked and pressure builds to move the actuator.

STUDY TIP

Fix the series-versus-parallel distinction in mind first; almost every other open center and closed-center difference follows from it.

KEY POINTS

  • Open center selector valves are connected in series.
  • Closed-center directional control valves are arranged in parallel.
  • Open center systems have flow but no pressure while the actuators are idle.

SOURCES

  • sources/ama-airframe/ch12.txt "Open Center Hydraulic Systems"
  • sources/ama-airframe/ch12.txt "Closed-Center Hydraulic Systems"
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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.