FAA Aviation Mechanic Airframe (AMA)Hydraulic and Pneumatic SystemsMedium
A technician is bench-testing a hydraulic valve removed from an aircraft. Testing shows the valve allows full, unrestricted flow in one direction but completely blocks flow in the opposite direction, with no flow at all permitted in reverse. Which component has the technician most likely identified?
- ASequence valve
- BPump unloading valve
- CSimple check valve
- DOrifice (restrictor) check valve
Show answer & explanationAnswer & explanation
Correct answer: C. Simple check valve
A simple check valve permits free flow in one direction and totally blocks flow in the reverse direction. This differs from an orifice check valve, which still allows a restricted (metered) reverse flow through a small orifice rather than blocking it completely.
Why the other options are wrong
- A. A sequence valve controls the order of operation of two actuators, not simple directional flow blocking.
- B. A pump unloading valve diverts pump output to reduce load on a fixed-displacement pump, unrelated to directional flow blocking.
- D. An orifice check valve allows restricted reverse flow through a small passage, not complete blockage.
Simple Check Valve
A one-way valve that allows free flow in one direction and completely stops flow in the reverse direction.
- No bypass or metering path in reverse direction
- Commonly a spring-loaded ball or poppet design
- Different from orifice check valve, which allows restricted reverse flow
Memory trick: Simple check valve = one-way street with a locked gate behind you