Hydraulic flap handle oddity

[DXB]

Has anyone ever had this problem before:   After putting in takeoff flaps (two pumps) on the ground, the flap handle slowly migrates back up on its own.  It is not the check valve that holds hydraulic fluid in the lines for the flaps beyond the pump, because the flaps stay down when the handle comes back up.  Otherwise the system works normally - exactly 4 pumps to full down, zero air in system, normal retraction speed of about 10 sec on the ground from full down to full up. 

I have stared at the diagram of the system below, and I can't fathom how this phenomenon could happen, so I clearly don't really understand the system.  Is the reservoir getting pressurized somehow?  The handle coming up itself isn't really a problem - I just want to make sure there's nothing going on that might affect brake function or make me fall out of the sky.  It is a '68C model.  

 

 

[Prior owner]

If the flaps truly stay down, then My SWAG is that the vent tube on your reservoir has a restriction..?

Remove the filler cap and pump the flaps down to check..

Edited April 24, 2019 by PilotCoyote

[DXB]

4 minutes ago, PilotCoyote said:

If the flaps truly stay down, then My SWAG is that the vent tube on your reservoir has a restriction..?

pull the filler cap off and pump the flaps down to check..

Yeah I wondered about that too, but in that case, shouldn't there be negative pressure in the reservoir after just pulling two pumps of fluid out of it? That should hold the handle down.    I actually have the 201 windshield so no easy way to open the top of the reservoir.  I guess I could open up the filler port on the engine side of the firewall - I'll try that.

[Prior owner]

I don’t have a drawing with me of the pump, but regardless of which way it moves, a negative pressure in the reservoir should raise the handle, since raising the handle draws fluid into the cylinder during normal operation. I could have it wrong though..I haven’t had my second cup of coffee yet

 

 

[Shadrach]

2 hours ago, DXB said:

Yeah I wondered about that too, but in that case, shouldn't there be negative pressure in the reservoir after just pulling two pumps of fluid out of it? That should hold the handle down.    I actually have the 201 windshield so no easy way to open the top of the reservoir.  I guess I could open up the filler port on the engine side of the firewall - I'll try that.

 Dev, if your handle is coming back up, the pump cylinder is filling with fluid. If the cylinder is filling with fluid and the flaps are not coming back up, then the fluid is coming from the reservoir. 

Edited April 24, 2019 by Shadrach

[Shadrach]

Also, if the reservoir vent was clogged, that would create a vacuum in the reservoir and would actually inhibit flow to the pump cylinder, which in turn would inhibit the the handle raising rather than facilitate it...

[Shadrach]

Do your flaps lock out at four pumps?

[DXB]

1 minute ago, Shadrach said:

Do your flaps lock out at four pumps?

Yup - hard as a rock, and I get exactly 4 pumps in whether I put them in continuously or stop after two and let the handle drift up for one of the pumps on its own.  If I put all 4 pumps in and leave handle down, it does not drift up as much, just a little, but you can't pump any further at that point.

[Shadrach]

23 minutes ago, DXB said:

Yup - hard as a rock, and I get exactly 4 pumps in whether I put them in continuously or stop after two and let the handle drift up for one of the pumps on its own.  If I put all 4 pumps in and leave handle down, it does not drift up as much, just a little, but you can't pump any further at that point.

So when it drifts up, is it locked out or can you push it down?

[DXB]

41 minutes ago, Shadrach said:

So when it drifts up, is it locked out or can you push it down?

I can push it down unless I've put in 4 full pumps already (in which case it doesn't drift up nearly as much).

[Prior owner]

2 hours ago, Shadrach said:

Also, if the reservoir vent was clogged, that would create a vacuum in the reservoir and would actually inhibit flow to the pump cylinder, which in turn would inhibit the the handle raising rather than facilitate it...

So, that means that he may have pressure in the reservoir? Perhaps hot brakes and a clogged vent could cause pressure in the reservoir?

[Shadrach]

33 minutes ago, PilotCoyote said:

So, that means that he may have pressure in the reservoir? Perhaps hot brakes and a clogged vent could cause pressure in the reservoir?

After replying to you I tried to envision a scenario where the reservoir was pressurized due to a blocked reservoir vent.  Maybe if the blockage would allow for a equalization on the ground but then hold sea level pressure as the plane climbs. Seems like a long shot. Could be mechanical. There is a spring in the cylinder, but it should be pushing the piston closed (Handel down).

im going to look at a spare I have in the hangar and rethink this later. 

[DXB]

4 minutes ago, Shadrach said:

After replying to you I tried to envision a scenario where the reservoir was pressurized due to a blocked reservoir vent.  Maybe if the blockage would allow for a equalization on the ground but then hold sea level pressure as the plane climbs. Seems like a long shot. Could be mechanical. There is a spring in the cylinder, but it should be pushing the piston closed (Handel down).

im going to look at a spare I have in the hangar and rethink this later. 

Maybe the spring in the cylinder is broken.  And maybe the spring is there to keep the piston from filling and the handle from coming up with gravity feed of the hydraulic fluid (maybe a long shot).  I'll rule out the pressurized reservoir next time I'm in the hangar by working it with the filler port wide open.  

[carusoam]

A similar thing will happen with older hydraulic pump jacks...

 

pump, pump, pump... the car is lifted...

Moments later, the pump handle is back in the air...

 

I am expecting there is some sort of seepage... but only enough to move the handle?

 

Does the flap indicator indicate any movement...?

It is probably a special design to hydraulic pumps... whatever part, hole, or vent isn’t working as designed anymore...

Looking forward to see what Ross finds out... 

Best regards,

-a-

[Shadrach]

@DXB 

So I dug out my spare flat pump today. I disassembled the pump side just to look it over and lubricate it. I have to say that the title of this thread is absolutely correct… Your situation is an “oddity”.  When properly assembled, the spring holds the piston all the way forward in the cylinder (that’s handle down position in the cockpit).  I can’t tell you what’s causing your handle to raise in-flight what I can tell you is that whatever is causing it is overpowering both gravity (lifting the handle) and the internal spring in the cylinder (see 1st image). I used our kitchen scale to see how many pounds of pressure were required to move the piston off its forward stop. The rod started to depress just over 6 pounds it was over 10 pounds (see 2nd image) at the midpoint and was off the scale’s 11lb max long before reaching the rear of the cylinder. I believe that your pump has one of the following problems:

1) Incorrect assembly of the piston and spring. Highly unlikely as it would require removal of the rod end and end cap. It’s also obvious that it doesn’t really seat properly. (See 3rd image)

2) Assembled without the spring. If I were a betting man, this is where I’d put my money.

3) Has a broken/corroded spring. This is a possibility but also unlikely. While the the spring is dry,  it has little exposure to moisture.

Is this a new issue for you?

Correct spring position

Scale at mid point.

Incorrect spring position.

Edited April 25, 2019 by Shadrach

[Prior owner]

Hmm...if the piston detaches from the shaft, the handle could rise. Would that be possible?

[DXB]

1 hour ago, Shadrach said:

@DXB 

So I dug out my spare flat pump today. I disassembled the pump side just to look it over and lubricate it. I have to say that the title of this thread is absolutely correct… Your situation is an “oddity”.  When properly assembled, the spring holds the piston all the way forward in the cylinder (that’s handle down position in the cockpit).  I can’t tell you what’s causing your handle to raise in-flight what I can tell you is that whatever is causing it is overpowering both gravity (lifting the handle) and the internal spring in the cylinder (see 1st image). I used our kitchen scale to see how many pounds of pressure were required to move the piston off its forward stop. The rod started to depress just over 6 pounds it was over 10 pounds (see 2nd image) at the midpoint and was off the scale’s 11lb max long before reaching the rear of the cylinder. I believe that your pump has one of the following problems:

1) Incorrect assembly of the piston and spring. Highly unlikely as it would require removal of the rod end and end cap. It’s also obvious that it doesn’t really seat properly. (See 3rd image)

2) Assembled without the spring. If I were a betting man, this is where I’d put my money.

3) Has a broken/corroded spring. This is a possibility but also unlikely. While the the spring is dry,  it has little exposure to moisture.

Is this a new issue for you?

Correct spring position

Scale at mid point.

Incorrect spring position.

Wow thanks for the in depth investigation Ross.  The pump was IRAN'd by a local MSC ~4 years ago because it leaked a bit.   It still had a small leak after that - I chose to throw up my hands and top off the reservoir occasionally rather than spend more money chasing it.  Looking back on it, this handle oddity has been there in lesser form for the last couple of years at least, only now it has become much more noticeable.  Yes I bet the spring is missing, and perhaps the O-ring has gotten less tight so that itdoesn't hold the position of the piston as well over time. Assuming I can rule out the pressurized reservoir,  this issue doesn't look dangerous to me regardless - the flaps stay down when commanded to do so in flight or on the ground.  Maybe I'll take it back to that same MSC this year for annual and ask them to address it (famous last words).  

[Shadrach]

18 minutes ago, DXB said:

Wow thanks for the in depth investigation Ross.  The pump was IRAN'd by a local MSC ~4 years ago because it leaked a bit.   It still had a small leak after that - I chose to throw up my hands and top off the reservoir occasionally rather than spend more money chasing it.  Looking back on it, this handle oddity has been there in lesser form for the last couple of years at least, only now it has become much more noticeable.  Yes I bet the spring is missing, and perhaps the O-ring has gotten less tight so that itdoesn't hold the position of the piston as well over time. Assuming I can rule out the pressurized reservoir,  this issue doesn't look dangerous to me regardless - the flaps stay down when commanded to do so in flight or on the ground.  Maybe I'll take it back to that same MSC this year for annual and ask them to address it (famous last words).  

It was no trouble. I had to pump nearby and was quite curious what might manifest such a symptom.  I don’t think there’s any danger in using it as is. It would drive me nuts on a personal level. 

If the spring is gone, you’ll likely need to source it as an owner produced a part. If I can help in anyway let me know.

[carusoam]

Ross,  you are a True MSer!

Pics and details to match!

Thanks for sharing.

Best regards,

-a-

[Shadrach]

16 hours ago, PilotCoyote said:

Hmm...if the piston detaches from the shaft, the handle could rise. Would that be possible?

Seems unlikely as it would have to overcome the mechanical friction of the system and the gravity acting on the handle.