PA32 gear failure. Possible causes?

Just an update. It appears the shuttle valve in the power pack is leaking. The rest of the system checks our fine. No leaks otherwise. This valve allows the gear to sag down over time when the gear is up. Mechanic did say this could result in gear locking issue.

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drotto said:
Just an update. It appears the shuttle valve in the power pack is leaking. The rest of the system checks our fine. No leaks otherwise. This valve allows the gear to sag down over time when the gear is up. Mechanic did say this could result in gear locking issue.

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That's the typical problem with those pumps.
 
ahkahn said:
For those that said the hydraulics hold the gear up, you are correct. I saw a couple of posts that said the hydraulics push it down, as well, and that is false. It is a gravity-loaded drop through a release of hydraulic pressure through the pump. All the emergency gear down does is release the hydraulic pressure through different manual valve.

My suspicion is that it was down and locked the whole time (even though the controllers wouldn't confirm). I've had this happen to my plane and it has either been a sensor or the indicator light was loose. I now make it a habit to push in all 3 lights when I lower the gear... just to save me that potential heart-stopping moment again. It probably vibrated back on when he turned base/final.

I've also gotten under the nose and cleaned off the sensors. There is one that you push in, and sometimes it gets sticky. I'd push/clean that one, as well. Make sure you clean everything under off with CorrosionX.

It is extremely difficult for a Piper gear to not come down due to the design of the system. The only thing that can keep it up is if it gets jammed or off-kilter, but chances are it wouldn't go up to begin with if that were the case. If it swings clean, it won't stick. If it were a hydraulic issue, it won't go all the way up.

Watch that the mechanic doesn't chase the yeti... they enjoy doing that. Just jack it up, swing it several times, and if it works consistently, you're good.
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I'm so proud of you...it seems like just yesterday you were buying your Lance...now you're growing up so fast! *sniff, sniff* :rofl:
 
ahkahn said:
For those that said the hydraulics hold the gear up, you are correct. I saw a couple of posts that said the hydraulics push it down, as well, and that is false. It is a gravity-loaded drop through a release of hydraulic pressure through the pump. All the emergency gear down does is release the hydraulic pressure through different manual valve.
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During normal operation the hydraulic pump powers the actuators in both "gear up" and "gear down" movements.




 
^^^^

I am looking at this diagram, and for the most part it makes sense, but what exactly does the shuttle valve do? Somehow I think there is a missing tube underneath the words gear up/ gear down.
 
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Looking at it more I think it makes sense now. See If I am right. When you put the gear up on the diagram the pump turns counterclockwise, pushing fluid into the right side of the system and the gear cylinders fill from the bottom moving the gear up. The shuttle valve moves to the right while the gear is moving up so excess fluid being pushed out of the upper part of the cylinders is returned to the reservoir. Eventually, the gear up check valve moves right and the pressure switch is pushed up.

On extension the pumps turn clockwise pressurizing the left side of the system, and moving the gear down. The shuttle valve is pushed to the left allowing fluid to fill the top portion of the cylinders. The check valve also moves left, and the pressure switch is released. Released pressure switch means green lights.

The other valves are just there to avoid over pressuring the system, over heating the system etc. Basically safety pressure relief. With a bad shuttle valve, the valve is staying too far to the left, and allowing fluid to move back into the left (or down) side of the system.
 
ahkahn said:
For those that said the hydraulics hold the gear up, you are correct. I saw a couple of posts that said the hydraulics push it down, as well, and that is false. It is a gravity-loaded drop through a release of hydraulic pressure through the pump. All the emergency gear down does is release the hydraulic pressure through different manual valve.
Click to expand...

ahkahn said:
AFIK, it is running the pump in reverse to accelerate the pressure release. Even without the pump, the emergency gear valve release allows it to lower the gear, albeit slower than with the pump functioning.
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Again in normal operation the system contains three double acting hydraulic cylinders. Primary power to move the gear in either retracting or extending positions is the hydraulic pump, not a spring, weight or aerodynamic forces.

Double acting hydraulic cylinders have two ports on them to supply pressure to either side of the piston, to extend or retract the ram.






 
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Yep, the pump runs in the same direction, up and down is determined by valve position
 
If the gear is retracted and the gear selector is moved to the down position the pump will run until all the downlock switches are actuated, indicating the gear is down and locked, because hydraulic force is used to ensure the gear is moved to down and locked.


 
tmyers said:
Yep, the pump runs in the same direction, up and down is determined by valve position
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Think the manual listed above says it is a reversable pump, that would indicate pumping direction, not a switch, controls up or down.

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drotto said:
Think the manual listed above says it is a reversable pump, that would indicate pumping direction, not a switch, controls up or down.

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He's incorrect. The gear selector reverses the motor.
 
tmyers said:
Dayum wrong again. That certainly makes the whole system simpler.
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It takes a while to figure them out. An early 210 has more stuff like a selector lockout solenoid on the handle, a gear door valve, door closed accumulator uplock and downlock actuators and all kinds of stuff.
 
I had the nose gear on a rented '84 PA-32R-301 hang up in mid-cycle, while retracting it after takeoff. I could hear the difference in the slipstream sound, and could tell the airplane wasn't cleaned up, so it wan't just a limit switch.

I was climbing out from KVNY through an overcast deck so I left it alone until I was on top, then canceled IFR and told ATC I needed to loiter in the area and work with it for a while. I slowed down, cycled the gear a couple of times and did the fishtail. That finally got three green, so I called ATC, got the ILS 16R approach, and returned to base. Never heard the mechanic's diagnosis.
 
Far I can tell the shuttle does nothing more than determine if the extend side or retract side is connected to the reservoir while in transit.
 
When there's a continuous gear motor noise when the gear is up and locked, the likely cause is u/s o-ring on the gear unlock valve. Change the ring and check the gear cycles once. It happened to me on the piper saratoga. I checked the shuttle valve and it didn't work till I chased the cause to the gear uplock valve
 
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