M20 Hydraulic Pump Flap Diagram

[Nukemzzz]

Giving back to the community here...

My M20e is grounded again while I sort out why the flaps won't stay down.  Three weeks ago the retract cable broke, I fixed that.  The flaps leaked up a little then but it seemed to be ok.  8hrs of flying later it retracts before you can complete touchdown on final which is dangerous...I had to take this bird apart yet again.   

To troubleshoot I hunted down all the info and pics that I could find on the forum and started creating a diagram of the system (I'm a mechanical engineer by trade working primarily with high pressure fluid flow and pumps so this is right up my alley).  Then I pulled my flap pump, opened up the bits I didn't see pictures for, and finished the diagram. 

I saw a lot of confusion on this topic, and some bad advice being given in some cases, and decided to complete my diagram and share it with you all to make it easier to help others take care of this part in the future. 

Attached is my first draft of this diagram. I'm providing it to help the community better understand this part, how it works, along with some troubleshooting guidance.  I'm sure I have typos, maybe an error in my logic somewhere, and some things I failed to include.  So I'm providing this draft to you all so you can help me finalize it for future use.

Let me know what you see wrong or if you think I should add something and I'll make edits and push out the new version.

Side Note:  I didn't research the actuator cylinder/piston since it wasn't my focus for this repair.  I took a guess at it's design.  So I'm counting on this part being wrong.

66' Money M20E Flap Pump Diagram.pdf

Edited April 13, 2020 by Nukemzzz

[carusoam]

Parts and maintenance manual should be your first stop...

If you select the wrong material because it looks the same... it can cause the same difficulty you are describing...

If you use a procedure that is different... you may have left out a step...

Yes, having the flaps snap back up as you slow on final approach is fall out of the sky dangerous... as the stall speed changes about 10mph... less than the safety bracket you are probably using...

Are you sure those are nylon washers in the pump to seal the oil flow from flowing past the ball bearing like unidirectional valves...

Or are they Teflon?

nylon has the ability to absorb moisture and oil where Teflon won’t... a plastic that absorbs a liquid will change dimension...

Nylon is pretty tough as well... and won’t readily conform to the spherical shape of the ball bearing... Teflon, on the other hand, forms a pretty good seal because of its softness...

Where some technical improvements could be made, but can’t without some STC documentation... the pump material is leather?   
 

Ross @Shadrach has documented some of the best details for flap maintenance... invite him to look over your shoulder...

PP thoughts only, I get concerned because I have had the flaps go from down to up in a snap... in my M20C... not a mechanic...

Best regards,

-a-
 

[Nukemzzz]

13 minutes ago, carusoam said:

Parts and maintenance manual should be your first stop...

If you select the wrong material because it looks the same... it can cause the same difficulty you are describing...

If you use a procedure that is different... you may have left out a step...

Yes, having the flaps snap back up as you slow on final approach is fall out of the sky dangerous... as the stall speed changes about 10mph... less than the safety bracket you are probably using...

Are you sure those are nylon washers in the pump to seal the oil flow from flowing past the ball bearing like unidirectional valves...

Or are they Teflon?

nylon has the ability to absorb moisture and oil where Teflon won’t... a plastic that absorbs a liquid will change dimension...

Nylon is pretty tough as well... and won’t readily conform to the spherical shape of the ball bearing... Teflon, on the other hand, forms a pretty good seal because of its softness...

Where some technical improvements could be made, but can’t without some STC documentation... the pump material is leather?   
 

Ross has documented some of the best details for flap maintenance... invite him to look over your shoulder...

PP thoughts only, I get concerned because I have had the flaps go from down to up in a snap... in my M20C... not a mechanic...

Best regards,

-a-
 

Fair point on the nylon verbiage. I didn’t intend on calling out the material. I’ll change it to “plastic”. 

On final the flaps would creep up in 10-15 seconds.  They also creeped up on the ground. It did it before the flap cable broke, but it was getting progressively worse. 

The other strange factor is the retraction speed adjustment screw has no impact on the retraction speed. I expected to find a broken spring in there...

This pump has been messed with before.  I think they messed it up but I’m not sure how yet.

[carusoam]

Many people find out the hard way regarding speed adjustment...

They often get set on the ground to a good speed... and then find out that flap raising speed changes a lot with wind forces...  the manual gives the time differences, but doesn’t get very specific...

 

I was so happy to have my flaps working... lots of rubber tube replacements and brake fluid clean outs... chasing the ball bearings across the floor...

I thought I was good with four pumps... one to pressurize the system and 3+ to move the flaps...

Then Ross showed us a video... there is no need for that first pump... we don’t actually pressurize the system...

By the time I learned this detail... it was years after my ownership...

+ 1 on some details you can learn from other MSers... I thought the plastic washer had a conic shape... apparently it starts out as a cylinder and changes pretty quickly in use...  oddly, I think it may have a Mooney part number and wasn’t very expensive...

+1 on setting the community up with some great learned knowledge...

Be sure to write something about your experience level, like...

PP thoughts only, not a mechanic... 

Best regards,

-a-

[Nukemzzz]

Actually, a ball seals fine on a sharp edge as well. The smaller the contact area between the ball and seat, the higher the contact pressure, and the less likely it is to leak. The reason you use a cone in a high pressure application is to keep from damaging the ball or seat but this isn’t an issue at these pressures  

They would have used plastic washers so they conform to the shape of the ball under load and because they will wear to fit even better over time.  There might be a tiny chamfer in the ID, I’ve not gotten that far yet. Just ordered the Lasar rebuild kit. 

Edited April 13, 2020 by Nukemzzz

[carusoam]

Hey good morning Nuke!

Quality of your sharp edge becomes extra expensive...

The slightest nick, scratch, dent, out of round, or speck of dirt would allow for an annoying leak...

The environment these things live in is not exactly clean room quality... especially when the little balls go bouncing across the ancient floor... (20 year old memory that is not going away)

The (traditional) documentation is pretty sparse .  No pics, few drawings... no HD or color to help...

Whenever there are two ways to assemble something, the errors become much larger...

keep up the good effort...

PP thoughts only, not a mechanic or legal document guy...

Best regards,

-a-

 

[N201MKTurbo]

#5 in your diagram is an aluminum seat, not steel.

You need to re-coin the steel ball on the aluminum seat. (#5) That will fix your leak down problem. I've never seen it be #4, but it could. If I recall the Teflon seats have through holes, so you can turn them over if the seat gets damaged.

[Nukemzzz]

50 minutes ago, N201MKTurbo said:

#5 in your diagram is an aluminum seat, not steel.

You need to re-coin the steel ball on the aluminum seat. (#5) That will fix your leak down problem. I've never seen it be #4, but it could. If I recall the Teflon seats have through holes, so you can turn them over if the seat gets damaged.

Aluminum...interesting. I’ve not been able to inspect it closely yet but having a easy to yield material tracks. It’s also easily damaged by debris or cavitation which is probably why it shows up as a cause so often on this forum. 

[Andy95W]

Nuke, thanks for taking the time to make the diagram and post it here.  Very helpful!

[Shadrach]

11 hours ago, Nukemzzz said:

Aluminum...interesting. I’ve not been able to inspect it closely yet but having a easy to yield material tracks. It’s also easily damaged by debris or cavitation which is probably why it shows up as a cause so often on this forum. 

The number one cause of hydraulic flap problems is improper assembly after maintenance. If you’re having trouble PM me your number so we can talk. It’s a simple and elegant system that works beautifully when properly set up. 

Edited April 14, 2020 by Shadrach

[Shadrach]

The diagram correctly illustrates the flow of fluid through the pump. However, I think it may be confusing to someone working on a an actual pump. While the flow illustration is correct, the location of the check valves does not resemble their actual orientation in the assembly body.

[Nukemzzz]

21 minutes ago, Shadrach said:

The diagram correctly illustrates the flow of fluid through the pump. However, I think it may be confusing to someone working on a an actual pump. While the flow illustration is correct, the location of the check valves does not resemble their actual orientation in the assembly body.

System diagrams often sacrifice spatial accuracy for the sake of understanding how the system works. I’m thinking of adding a page two that points out where these things are on the actual pump. 

Edited April 14, 2020 by Nukemzzz

[Nukemzzz]

37 minutes ago, Shadrach said:

The number one cause of hydraulic flap problems is improper assembly after maintenance. If you’re having trouble PM me your number so we can talk. It’s a simple and elegant system that works beautifully when properly set up. 

This is demonstrably false since pumps had to have had something fail in the first place that caused them to to need servicing...for them to be assembled wrong. 

[Shadrach]

2 hours ago, Nukemzzz said:

This is demonstrably false since pumps had to have had something fail in the first place that caused them to to need servicing...for them to be assembled wrong. 

Pumps weep fluid. Sometimes from air vents at actuator. IA sees evidence of leak. Insists assembly must be resealed. Flaps never work the same again.  Good luck Nuke, you’re demonstrably sure enough of yourself to tackle this. 

Edited April 14, 2020 by Shadrach

[carusoam]

Nuke,

That’s mostly true, but...

you haven’t had something maintained yet that didn’t need it?

Then have it taken apart and not put back together properly...?

Try to be nice to the one guy who is most familiar with the flap pump... we may need him again.

Best regards,

-a-

[Shadrach]

12 minutes ago, Nukemzzz said:

System diagrams often sacrifice spatial accuracy for the sake of understanding how the system works. 

I retract my criticism. There’s no room for improvement.

[Nukemzzz]

Don’t expect me to be nice to someone that shows up, adds no value to the conversation, and only ads dismissive criticism.  My reply was actually less rude than his.  I was simply as blunt as him...doesn’t read well does it?

I’ve spent the last 18 of my 20 professional years designing and launching pumps that work like this, but operate at 1800RPM pushing over 30,000PSI.  Prior to that I spent 9 years professionally fixing similar systems. So yes, So yes, I’m confident in my ability to make a diagram of this extremely primitive and simple hydraulic pump design.  And I don’t need rude pearls of wisdom. 

Try injecting some tact into your posts. They will be received better. 

For the record it has some design flaws. It’s not a perfect elegant system, for one the retract circuit sensitivity it too high.  But that’s not the point of this thread.

Edited April 14, 2020 by Nukemzzz

[Shadrach]

2 hours ago, carusoam said:

Nuke,

That’s mostly true, but...

you haven’t had something maintained yet that didn’t need it?

Then have it taken apart and not put back together properly...?

Try to be nice to the one guy who is most familiar with the flap pump... we may need him again.

Best regards,

-a-

I’m sure there are others that know more than me, but most of them cost a lot more. Some cost more and are clueless. Last guy I spoke with about flaps paid an a&p to reassemble system that was sent to Lasar for OH. Flaps kept retracting on climb out.  I knew immediately when I spoke with the owner that the elevator controls were interfering with the retraction cable. After two calls he identified what had happened. That pro had mounted the retraction cable to the elevator pushrod.   I have seen all manner of of bizarre mx performed on this system, but that was the worst. It’s not so critical that the plane can’t be operated without properly functioning flaps. Which is nice because I would estimate 10-15% of the fleet is out of rig and/or not properly bled.

Edited April 14, 2020 by Shadrach

[Shadrach]

Just now, Nukemzzz said:

Don’t expect me to be nice to someone that shows up, adds no value to the conversation, and only ads dismissive criticism.  My reply was actually less rude than his.  I was simply as blunt as him...doesn’t read well does it?

I’ve spent the last 18 of my 20 professional years designing and launching pumps that work like this, but operate at 1800RPM pushing over 30,000PSI.  Prior to that I spent 9 years professionally fixing similar systems. So yes, I’m demonstrably confident in my ability to make a diagram of this extremely primitive and simple hydraulic pump design.  And I don’t need rude pearls of wisdom. 

Try injecting some tact into your posts. They will be received better. 

For the record it has some design flaws. It’s not a perfect elegant system, for one the retract circuit sensitivity it too high.  But that’s not the point of this thread.

Do quote where I was rude? Where was I dismissive?  There was no malice in my post. I stand by the fact that your depiction might very well confuse someone looking at an actual assembly.  I have helped dozens of owners, A&Ps and IAs with this system. My experience came from the fact that my system was overhauled and returned to service no longer leaking but not operating as it had prior to removal. After an addition 5 hours of shop time it was only marginally better. I completely removed the system, disassembled, reinstalled under supervision.  That was 16 years ago. I have since overhauled the assembly again. I have also volunteered my time to help many others via  PM, phone and in person. The system is not complicated yet it confounds intelligent and credentialed people at times. It seems you were fishing for an attaboy with your diagram and I disappointed you. My apologies. Given your impressive credentials, you’ll likely have no problems sorting out such a simple system. 

[Shadrach]

23 minutes ago, Nukemzzz said:

Don’t expect me to be nice to someone that shows up, adds no value to the conversation, and only ads dismissive criticism.  My reply was actually less rude than his.  I was simply as blunt as him...doesn’t read well does it?

I’ve spent the last 18 of my 20 professional years designing and launching pumps that work like this, but operate at 1800RPM pushing over 30,000PSI.  Prior to that I spent 9 years professionally fixing similar systems. So yes, I’m demonstrably confident in my ability to make a diagram of this extremely primitive and simple hydraulic pump design.  And I don’t need rude pearls of wisdom. 

Try injecting some tact into your posts. They will be received better. 

For the record it has some design flaws. It’s not a perfect elegant system, for one the retract circuit sensitivity it too high.  But that’s not the point of this thread.

It’s fine, especially given the tight work space. Just takes a light touch. 

[Andy95W]

22 minutes ago, Shadrach said:

Do quote where I was rude? Where was I dismissive?  

Well, maybe not necessarily rude, but a little sarcastic... twice...  

But my message to Nuke:  Ross (Shadrach) is one of the 3 most knowledgeable guys on this site when it comes to hydraulic flaps.  He's a really good person to listen to about them.

And with that said- I've disassembled and repaired 3 hydraulic flap actuators.  2 of them actually needed it.  I understand the system pretty well.  And I still found your schematic sketch helpful in understanding the system better.

[Shadrach]

4 minutes ago, Andy95W said:

Well, maybe not necessarily rude, but a little sarcastic... twice...

But my message to Nuke:  Ross (Shadrach) is one of the 3 most knowledgeable guys on this site when it comes to hydraulic flaps.  He's a really good person to listen to about them.

And with that said, I've disassembled and repaired 3 hydraulic flap actuators.  2 of them actually needed it.  I understand the system pretty well.  And I still found your schematic sketch helpful in understanding the system better.

Indeed that’s true but only after the the snarky reply. Just trying to keep up...

Edited April 14, 2020 by Shadrach

[Nukemzzz]

32 minutes ago, Shadrach said:

Do quote where I was rude? Where was I dismissive?  There was no malice in my post. I stand by the fact that your depiction might very well confuse someone looking at an actual assembly.  I have helped dozens of owners, A&Ps and IAs with this system. My experience came from the fact that my system was overhauled and returned to service no longer leaking but not operating as it had prior to removal. After an addition 5 hours of shop time it was only marginally better. I completely removed the system, disassembled, reinstalled under supervision.  That was 16 years ago. I have since overhauled the assembly again. I have also volunteered my time to help many others via  PM, phone and in person. The system is not complicated yet it confounds intelligent and credentialed people at times. It seems you were fishing for an attaboy with your diagram and I disappointed you. My apologies. Given your impressive credentials, you’ll likely have no problems sorting out such a simple system. 

I think stay at home has me over reacting a bit. Reading in to things. 

The first comment about the layout seemed petty to me.  The second comment seemed to disregard the value of my effort because the issue is always misassembly. Like I was wasting my time. 

When I developed issues with my flaps I went through the forums. They are extremely valuable to folks like me. I went through all the posts on this. What I saw was about a 50% hit rate on good advice driven largely by a misunderstanding of how the pump worked. Someone in need doesn’t know who to believe.  They have to decide that for themselves and it helps if they have a way to understand the parts themselves in a simple format  this post was a way to get agreement on: “yep, that’s how it works”  

I think this forum is a major contributor to the future survival of these vintage birds.  Mooney isn’t going to give us the prints or make diagrams for us. It falls on folks like you and I to gather and retain knowledge for others. We can each do our part. While I can’t make a circuit board diagram or tell someone how to do upholstery, I’m uniquely qualified for explaining how a hydraulic system works. So I’m contributing how I can.  
 

I am sorry if I misread your intentions. I’ll delete all my comments after you get a chance to see this one. 

Edited April 14, 2020 by Nukemzzz

[Shadrach]

19 minutes ago, Nukemzzz said:

I think stay at home has me over reacting a bit. Reading in to things. 

The first comment about the layout seemed petty to me.  The second comment seemed to disregard the value of my effort because the issue is always misassembly. Like I was wasting my time. 

When I developed issues with my flaps I went through the forums. They are extremely valuable to folks like me. I went through all the posts on this. What I saw was about a 50% hit rate on good advice driven largely by a misunderstanding of how the pump worked. Someone in need doesn’t know who to believe.  They have to decide that for themselves and it helps if they have a way to understand the parts themselves in a simple format  this post was a way to get agreement on: “yep, that’s how it works”  

I think this forum is a major contributor to the future survival of these vintage birds.  Mooney isn’t going to give us the prints or make diagrams for us. It falls on folks like you and I to gather and retain knowledge for others. We can each do our part. While I can’t make a circuit board diagram or tell someone how to do upholstery, I’m uniquely qualified for explaining how a hydraulic system works. So I’m contributing how I can.  
 

I am sorry if I misread your intentions. I’ll delete all my comments after you get a chance to see this one. 

Context is a challenge on line. My wife would say that I can come off as gruff in person. Those two things can make for miscommunications. You’re not the first to read me as being rude when it was not my intent.  Indeed we agree that this place is critical to keeping our old birds flying. No need to delete your comments, people have said way worse to me. My apologies for not being more tactful.  

My offer stands. If you run into a “gumption trap” during your endeavors, give me a call. I’m on Eastern time.

Tree 0 one Fife zero 2 tree niner two fowah.

Edited April 14, 2020 by Shadrach

[Nukemzzz]

By uniquely qualified I mean...

I’ve been a mechanical engineer for diesel fuel injection systems for 18yrs. 6 of those years leading the development and launch of these systems into Europe. 2yrs Prior to the 18 I was a service engineer explaining to technicians around the world how to troubleshoot Diesel engines (creating diagrams and steps like attached...but more professionally done...not in PowerPoint). The 9 years before that I was a certified auto/diesel technician. My current job is an engineering reliability leader and manager for the same systems. The majority of this current job consists of engineers presentIng to me their troubleshooting of design failures trying to convince me that they know what went wrong and how to fix it (answer is often no...lol).