Hydraulic flaps won’t stay down.

[bixmooney]

Hi, 

I have a C model and I had some intermittent flap issues and they have progressed where the flaps won’t stay down often.     I have tested on the ground as well and sometimes they pump down and stay firm and other times not.   It seems like there may be particulate in the fluid to me. 

Is it a major thing to rebuild the hydraulic valve and pump ?    Curious if anyone else has had this problem. 
 

 

[Shadrach]

2 hours ago, bixmooney said:

Hi, 

I have a C model and I had some intermittent flap issues and they have progressed where the flaps won’t stay down often.     I have tested on the ground as well and sometimes they pump down and stay firm and other times not.   It seems like there may be particulate in the fluid to me. 

Is it a major thing to rebuild the hydraulic valve and pump ?    Curious if anyone else has had this problem. 
 

 

First step is to check that the flap release cable (#67 in diagram below) is correctly adjusted and properly secured at the pump (red arrow under #51).  

 

The release cable is attached to an arm (red arrow) that rotates a cam shaft that unseats the check valve for the return circuit.  You and your mx need to ensure that the valve is off the cam with the cable in the down position. If this does not solve your problem, then you likely have a valve leaking back to the reservoir.

[bixmooney]

Thank you Shadrach

will be checking it out and let you know what shakes out. 
 

 

Edited September 5, 2023 by bixmooney

[M20F]

Also it is hard to tell but there are 2 springs.  HE-1516 and HE-1516-1.  They are not interchangeable.  One is strong and one is weak. 

[bixmooney]

thank you , and will keep that in mind.

[bixmooney]

Hi, I haven’t made too much progress , but got to the reservoir and did add some fluid and made my way down to the valve assembly and took pictures of the cable ‘open’ and ‘closed’.   Open =the flaps set to retract and closed=set to pump them down. 
 

it doesn’t look like a lot of travel happens with the cable at the valve assembly.   
is that similar to what you see ? 

my mechanic is out of town for the week and don’t want to get over my head.  

[N201MKTurbo]

It looks like the cable conduit has slipped in its clamp. That clamp doesn't look like it is adequate for clamping the cable. That type of clamp needs to fit the cable tighty. Using some fabric tape to take up the space will not let it clamp the cable tight enough.

[Fly Boomer]

2 minutes ago, N201MKTurbo said:

It looks like the cable conduit has slipped in its clamp. That clamp doesn't look like it is adequate for clamping the cable. That type of clamp needs to fit the cable tighty. Using some fabric tape to take up the space will not let it clamp the cable tight enough.

Looks like two different types of cable sheath with a goober of something (RTF?) around the junction that used to be hidden by the clamp?

[bixmooney]

21 minutes ago, Fly Boomer said:

Looks like two different types of cable sheath with a goober of something (RTF?) around the junction that used to be hidden by the clamp?

I am seeing that now and the slip appearance too.  
 

I think I will disengage it and test the valve by itself and see if it holds pressure.   Thank you 

[N201MKTurbo]

This looks like the proper clamp. You need to measure the cable to get the right size.

https://www.aircraftspruce.com/catalog/appages/extgrp-condclamp.php?clickkey=8079

 

These clamps have the dent in them to hold the conduit in place. It looks like you have a stangard AN742 clamp, that doesn't have the dent.

 

[bixmooney]

1 hour ago, bixmooney said:

I am seeing that now and the slip appearance too.  
 

I think I will disengage it and test the valve by itself and see if it holds pressure.   Thank you 

Definitely the cable and linkage.    It’s tough to get to the backside without taking off more skin from the bottom of the plane 

 

the cable has always felt ‘gummy’ and not sliding freely when putting flaps up and down.    I will get the help of my mechanic when he is able and replace the whole cable too 

 

[Shadrach]

4 minutes ago, bixmooney said:

Definitely the cable and linkage.    It’s tough to get to the backside without taking off more skin from the bottom of the plane 

 

the cable has always felt ‘gummy’ and not sliding freely when putting flaps up and down.    I will get the help of my mechanic when he is able and replace the whole cable too 

 

I don't see a much if any movement in the cable sheath relative to the clamp. I count 13 windings from the clamp to the cable end in both images.  However, that does not mean that the cable is properly lubed and adjusted.

The low hanging fruit is to try to manipulate the arm into a position where the flaps will hold. If you can manage to make them work, I lubricate the cable with a low viscosity lubricant.  The cable sheath is not covered so it should be easy to lube wherever it is exposed. I like Mouse milk or Kroil for this type of application. It should not feel wooly or gummy but it's not rifle bolt precise either.

It's clear that the pump is weeping a small amount of fluid where the two halves mate together.  I would not overhaul a pump just for a small seep, but if the system cannot be made to function, that is the next step.