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Help Diagnose My Hydraulic Flaps, Please!


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Picked up a M20G late last year and have been loving ownership so far. Lurked on here for a good while prior to finding the one for me--reading about the planes, potential issues, ect--so thank you to everyone for the plethora of information. But it is plane ownership so something has to go wrong eventually, right?

A month or two after pick up, the flaps slowly stopped working, going from sometimes getting half deployment to nothing at all with a springy handle. In reading all of the other threads on the topic, it seemed like a leak somewhere in the system so I topped off the reservoir, pumped the flaps a million times and eventually got full deployment back. Red fluid drips on the belly confirmed a leak. Over the next two months, the same cycle happened 2 or 3 times, flaps would stop working, top it off, pump a million times, flaps start working. Finally got a temperate day to spend some time poking around the belly panels and took a look at the pump to see a hydraulic fluid drip up on it, so got on a mechanic's schedule to have him take a look. He wasn't convinced that the pump was leaking enough to force me to top off once or twice a month but he inspected the rest of the hydraulics and couldn't find anything obvious so I had him overhaul the pump since it was our only lead so to speak.

Flew her home with working flaps. Then had to wait a few weeks due to winter weather before getting to fly again and lo and behold, no flaps again. Topped off the reservoir, pumped a million times and got pressure back in the handle but the flaps don't move at all (they move when you push on them outside). Eventually, after a lot of pumping and attempting to cycle the pressure from the handle dropped off and returned to the spring back state which I assume is a vacuum in the pump based on all of the other threads that I read through. Crawled around under the plane taking a look at various panels to see if there was anything new or obvious but the pump was perfectly clean and no fluid below it. Looked at the actuator, didn't see any issues or apparently leaks there either. Log books only mention one hose being replaced sometime in the last ten years but all of them look fairly new or they don't fit the hard and bubbly description I've read on here. I guess at this point the only other option would be the actuator considering that's the last piece that hasn't been touched in the last decade (or at least I couldn't find any mention of it in the log books).

When the flaps did work, they were solid, no slow leak up, handle stayed put and at time of purchase was 4.5 pumps to full flaps, great timing in the air and on the ground, just couldn't contain the hydraulic fluid apparently. 

Anyway, going to take a look with him in a week or two if schedules line up, figured I should get ahead of it and see if anyone had thoughts on it or had recommendations on what to take a peek at. Appreciate it in advance.

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The brakes share the hydraulic fluid with the flaps so you might expand your troubleshooting.  In umpteen years of G ownership I haven't had an issue with either system, but I've read the stories where it was a real bugger to track down an issue.  Good luck.

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Brakes pulls fluid from lower in the reservoir than the flaps, right? Fortunately, have not had any issues with the brakes themselves but a good idea to give them a good look over. Hoping it doesn't turn into a guessing game.

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The brake system splits from the flaps well ahead of the flap pump. The components are rebuildable in the field but it may be best to send it to Maxwell Aviation or LASAR for overhaul and testing. 

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The flaps are a closed system. 1 pump and fluid goes down the line to the actuator and a check ball closes it off from returning to the pump after you start to pull the handle back up for the next pump. Do that 4 times or so and the pumped fluid drives the actuator out to put the flaps down and the check ball keeps the fluid trapped in the line from the pump to the actuator. Hard hydraulic lock to keep them down. 

When you pull the flap control handle up to raise the flaps it causes the check ball to release the trapped fluid and the return spring on the flaps pulls them up as the fluid returns through the same line it went down going back into the reservoir. 

You  say you had the pump worked on OK If you have no leaks at the actuator then you have air in the system or the check ball is not working properly in the pump system. The flap control handle is not adjusted properly to unseat the ball when in the flaps up position and to let it seat when in the flaps down position. 

Getting all the air out in these flaps can be a bear. 2 people and lots of fluid being pumped down to the actuator line connection. 

Make sure of your supply to the pump by pulling the line to see if fluid flows. 

Use plenty of towel and rags on the floor and nose tire tunnel for the inevitable red fluid leaks you'll be causing 

I suspect you have air in the system or the check balls are not adjusted properly in the pump.

Remember to keep filling the reservoir as it is very small and you can draw more air into the system if it runs dry. 

 

 

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I would say the pump was the issue and the rebuild (the o rings) fixed it.  Now you just need to bleed the system to get the air out.  
 
It is always going to leak a bit from the felt rings so be mindful once a year to dump in a little 5606 into the reservoir.  If it never gets low you won’t get air.  Once though it gets below the break point between flaps/brakes though you are bleeding and it is messy unless you make some fittings up. 

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