Auto-Pilot Elevator Control Valve

Inoperative #1 auto-pilot. Flight fault review showed numerous "ELEV ENG TST A" and "ELEV ENG TST B" failures for both the Left Inboard and Right Outboard elevators.

From the Fault Isolation Manual: Power up test failure. The FCC could not successfully verify the proper operation of the Electro-Hydraulic Valve (EHV).

I ran a CFDS test of the #1 elevator system. Everything passed, but we had one control valve on hand...... we chose to change the left inboard elevator valve.

One panel to drop.



Control valve is the non-tapered one which is actually inboard. View is looking up with the image bottom being outboard.



Some safety wire cutting and four allen screws later.....valve off. (The control valve is hydraulically "downstream" from the shut-off valve. We didn't blow reservoir head pressure before removing the valve, but you always get somewhat squeamish before un-mounting any hydraulic components. We lost around 20 drops total.)


Removed valve in shop. One (lower) pressure input port and two output ports. One for elevator up..... one for down. The electrical connector is internal in the actuator. It's rare, but sometimes a wire breaks inside the main actuator..... it can be verified with a meter from the main actuator interface plugs to the "mini" valve connectors. Any opens in wire continuity require the whole damn actuator to be replaced.



MD-11 Fault Isolation Manual 22-00 Task 848-850
AMM Valve Replacement 27-33-21-4

No pictures, but the seals were somewhat of a bitch. A small o-ring encompassed inside a nylon ring. Tiny and very hard to "seat" in the port recess areas.
Safety wiring the screws was the cause of a few cuss words also.

Had an MD sitting all day ready to fly, and we come in to do our walk around to find this very valve leaking. It had a large puddle under the elevator. Oh well!