FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
A hydraulic circuit uses a four-way selector valve to control a double-acting landing gear actuator. When the valve is positioned for gear retraction, what must it simultaneously accomplish?
- ADirect pressurized fluid to both actuator ports at the same time
- BRoute return fluid directly to the pump inlet, bypassing the reservoir
- CBlock flow to both actuator ports to lock the gear in its current position
- DDirect pressurized fluid to the retract side of the actuator while opening the extend side to return
Show answer & explanationAnswer & explanation
Correct answer: D. Direct pressurized fluid to the retract side of the actuator while opening the extend side to return
A four-way selector valve controlling a double-acting actuator must pressurize one side of the piston while simultaneously opening the opposite side to return flow. This allows the piston to move in the commanded direction without fluid being trapped or fighting itself on the opposite side.
Why the other options are wrong
- A. Pressurizing both sides simultaneously would lock the actuator, not move it.
- B. Return fluid goes to the reservoir, not directly back to pump inlet, bypassing filtration.
- C. Blocking both ports is the neutral/hold position, not retract.
Four-Way Selector Valve
A directional control valve with four ports that routes pressurized fluid to one side of a double-acting actuator while opening the opposite side to return.
- Controls direction of double-acting actuators
- Has pressure, return, and two actuator ports
- Neutral position often blocks both actuator ports to hold position
Memory trick: Four-way valve = four doors, only two open at once in opposite flow.