Manual Flaps leak back up.

[mikesalman]

Hi folks my manual flaps keep leaking back up. I notice halfway down the runway I have half of my t/o flaps still left. In downwind I put t/o flaps and on final with runway made I use full flaps. By the time I reach the taxiway I have 1/2 of my t/o flaps left. What could possibly cause them to leak back like that. I know the lever is in the closed position. Where would I look for the cause. They go down good when pumped but will slowly bleed back when parked and much faster with wind flowing past them.

1968 M20F with approximately  2700 TT. Thanks

[Sven]

It's an adjustment issue. On the flap pump there is a slotted screw (standard) surrounded by a lock nut. Loosen the lock nut and turn the screw to the right (in) just a butt whisker, as my grandfather would say. Then try the flaps. It's best to have a friend cycle the flaps while you make the adjustment or you'll get very tired. I think the manual says you want a 10-12 second return from full down to full up. When you have it fully down you can apply some up pressure to simulate the wind and see if they drift up. If they do adjust the screw in a little more. If that doesn't work you might have a bubble in the system or maybe your fluid is low. That's what has worked on our speedbird.

[robert7467]

Mine was doing the same thing. We bled them, and adjusted that screw, and everything is fine.

[N601RX]

The screw mentioned above only controls how fast they come up when you release them. It sounds like your release cable is out of adjustment or your flap pump needs some new orings.

[robert7467]

When I was having the same issue, I called a MSC who also sells parts, and he said it was pretty much a crap shoot when it comes to changing the orings.

[Bob_Belville]

A few months ago I thought I had the same problem but on more careful examination found that the valve lever was not going all the way down. It felt down but was not. After vigorously cycling the level a few times it held pressure. (I only have 2500 hours flying with this flap system. Still screwing up.) But of course YMMV.

[eaglebkh]

I had the same problem.  Topping of the fluid might help.  But if you have a fluid leak, the investigation begins.  I had to replace my pump with a LASAR OH'd one.

[rockydoc]

What is the best way to get access to the flap pump and its adjustment screw.  Also, what is the procedure for bleeding the system?  Thanks for the info.

[robert7467]

Its been so long ago, but it should be in the service manual, if you need one, I have a copy I can email you. But basically, you pump the faps until all the air is out of the lines, you might need to bleed your breaks as well since its on the same system.

[N201MKTurbo]

OK, if the flaps are bleeding up, it must be the check valve in the flap pump. There is a small pin that the cable pushes to push the ball off its seat. It is not an o-ring problem. Either the ball or seat is dirty or the seat is damaged. You can repair the seat by re-coining it by putting the ball in the seat and whacking it real hard with a punch and hammer (on the bench not in the plane).

 

BTW don't stretch or replace the spring on the check valve ball, or your flaps won't work at high elevation airports.