My hydraulic pump has started to short cycle, cycles about every 45-60 sec. Inspection shows no external or internal leakage, however after some experimentation, turns out it only cycles about every 5-6 min airborne with the gear handle UP. Flap position does not seem to make a difference. Seems to me a good place to start is the gear valve, I'm thinking it's by-passing internally. It could be an actuator bypassing in the down position, but I think that would more likely show up as a leak.
Consulting the build manual all it shows is the gear and flap valves bolt onto the central valve body with o-rings sealing the mating surfaces. I did not build this plane, nor have I ever had a reason, up till now, to access these valves. Question for those familiar with these controls: Can the gear and flap valves rebuilt, or just replaced? Can they be rebuilt in the field or need be sent off somewhere? Any "gotchas" associated with removal/installation?
Thanks for any input.
Rock
Hydraulic Valves
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Tom Sullivan
- Posts: 80
- Joined: Mon Nov 28, 2022 2:33 pm
I tore mine apart for a similar issue. I removed it to work on it but otherwise it wasn’t real complicated. I found the valve is actually a flat disc and o-ring that aligns with ports to move the fluid appropriately. I found a minor scratch on one of my flat discs and sanded it out with 600 grit, then 1,000 grit sandpaper and reassembled it. That fixed my problem.
I actually have hydraulic gauges for my up and down functions of my gear so I can monitor what’s actually happening with my pump and pressures. It allows me to verify the hysteresis is correct. That same feature on my door seal verified a pressure control was too sensitive, creating the same issue with the door seal. I installed an adjustable pressure switch (adjustable for both high and low limits), virtually eliminating that problem.
Tom
I actually have hydraulic gauges for my up and down functions of my gear so I can monitor what’s actually happening with my pump and pressures. It allows me to verify the hysteresis is correct. That same feature on my door seal verified a pressure control was too sensitive, creating the same issue with the door seal. I installed an adjustable pressure switch (adjustable for both high and low limits), virtually eliminating that problem.
Tom
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Rock Barchfeld
- Posts: 22
- Joined: Fri Nov 03, 2023 11:49 am
You Da Man! Your description describes what I had envisioned from the Build Manual. As near as I can determine, my valves have been untouched since 2009, (more likely much earlier). I suspect my issue is worn, 15 year old, O-Rings, but you never know. Should you wish to achieve "Godlike Status", you could provide me an O-Ring size and "Dash" number... Just kidding, I was a product engineer for a hydraulic company, so have a little background on O-Rings.
Thanks for confirming my suspicions, I hope the fly in at Pelston comes together, see you there.
Rock
Thanks for confirming my suspicions, I hope the fly in at Pelston comes together, see you there.
Rock
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Tom Sullivan
- Posts: 80
- Joined: Mon Nov 28, 2022 2:33 pm
Rock,
"God like status" is not happening on this one.
I never documented the o-ring sizes, as I was able to reuse them. Maybe YOU could document them when you tackle this project and get that status yourself. 
I'm checking with Matt Speare on the status of the Pellston Fly-in. I have some logistical issues to straighten out but at about an 80% chance I will make it, if it's not cancelled.
Tom
"God like status" is not happening on this one.
I never documented the o-ring sizes, as I was able to reuse them. Maybe YOU could document them when you tackle this project and get that status yourself. I'm checking with Matt Speare on the status of the Pellston Fly-in. I have some logistical issues to straighten out but at about an 80% chance I will make it, if it's not cancelled.
Tom