Hydraulic flaps not coming down right away

[AlexLev]

Just got my plane out of its first annual..

On my preflight and flight back, I noticed that the hydraulic flaps are not operating like they used to. It takes me about 3 pumps to "prime them" before they start working as normal, otherwise there is no pressure when I immediately put the lever on down and begin pumping.

They did bleed my brakes as part of the annual, I wonder if it's a simple issue as the fluid being low or maybe the cold temps causing some issues? It was about 15F when I flew out.

Any idea what it could it be or what I could check?

Edited December 15, 2017 by AlexLev

[Sabremech]

I had a similar experience with my C after changing the hoses in the flaps and brake systems. Check fluid level and actuate flaps in the hangar up and down. Takes a while but mine work as advertised now. 

David

[AlexLev]

1 hour ago, Sabremech said:

I had a similar experience with my C after changing the hoses in the flaps and brake systems. Check fluid level and actuate flaps in the hangar up and down. Takes a while but mine work as advertised now. 

David

Thanks, David. We did actually swap some brake lines and hoses. When you say actuate flaps, do you just mean to continually pump them down and bring them up and just try to resolve the problem like that if the fluid levels are good?

[N201MKTurbo]

You need to bleed the flaps. 

They will usually get better by themselves by actuating them a bunch of times as stated above.

I have found it works faster if you do it at high altitude. If you need to waste some avgas climb to 12000 or so, slow to flap speed and put them up and down a bunch of times.

[Sabremech]

1 hour ago, AlexLev said:

Thanks, David. We did actually swap some brake lines and hoses. When you say actuate flaps, do you just mean to continually pump them down and bring them up and just try to resolve the problem like that if the fluid levels are good?

Hi Alex,

Yep

[AlexLev]

Thanks guys!

[AlexLev]

50 minutes ago, N201MKTurbo said:

You need to bleed the flaps. 

They will usually get better by themselves by actuating them a bunch of times as stated above.

I have found it works faster if you do it at high altitude. If you need to waste some avgas climb to 12000 or so, slow to flap speed and put them up and down a bunch of times.

That's interesting. Why is that the case?

[N201MKTurbo]

2 hours ago, AlexLev said:

That's interesting. Why is that the case?

My theory is that it makes the air bubbles in the lines much bigger, so they move through the system faster.

The reason the flaps get better by themselves is that unlike the brakes they move a relatively large volume of fluid in and out of the system each actuation. The more you move the fluid the more it encourages the bubbles to migrate to the high point in the system which is the reservoir where they can escape through the vent.

For the nerds:

https://physics.stackexchange.com/questions/228202/how-to-move-a-bubble-which-is-trapped-by-the-capillary-pressure

Edited December 15, 2017 by N201MKTurbo

[65MooneyPilot]

Sounds like air got into the system. The breaks and the flaps share the same reservoir.

[carusoam]

Lots of air bubbles....in the system...

Often self clearing with lots of use.

Use caution, the brakes are using the same hydraulic fluid.  

Depending on how much air is in the system and how it got in there, the brakes can be at risk as well...

We have a thread or three about how to bleed the system too...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[tony]

On 12/16/2017 at 11:59 AM, 65MooneyPilot said:

Sounds like air got into the system. The breaks and the flaps share the same reservoir.

They share the same reservoir but they are two independent systems.  The tap for the flaps  is on the side of the reservoir while the brakes come out the bottom.  If you have air in the flap system, doubtful it will affect the brakes unless the reservoir is completely dry.  

[Captnmack]

Attach a pressure pot, you can use a clean garden sprayer with a tube attached over the end and the other end over the brake bleeder port. Get some rags or other means to catch the spill over at the reservoir. If you have a sloped windshield this might be harder. Anyway, slightly pressurize the sprayer and open the Bleeder port and the cap on the reservoir and let run over slowly. Always use clean 5606 when doing this. IF, this does not solve the issue, then the O'rings in the Flap Actuator are bypassing.The kit is about $10 from Lasar and not too difficult to replace. Goodluck.