Bleeding/refilling hydraulic flap system

[M20F-1968]

I changed out my hydraulic flap pump  about a year ago but it was not acting correctly.   The first  pump of the day was ineffective,  then it acted normally for the rest of the day with four pumps to lockup as it should.   However,  after several days of sitting the problem occurred.

 I had my belly pan off recently and decided to readdress this issue.   I tried  attach  a pressure pot to the aft end of the system by removing the cap on the T fitting and pushing hydraulic fluid forward.   With this  procedure alone the system became unresponsive and there was clearly air in the flap pump.

 I went back to the manuals,  reviewed what I had done in the past,  and decided to make connection hoses so that I had an option pushing hydraulic fluid from the front to the back,  as well as the back to the front.   These consisted of appropriate hoses  to the various AN fittings.   I also installed a pressure gauge onto my pressure pot.   The Mooney  suggests pushing fluid in the 30 to 40 psi range.

 The manual states  that fluid should be pushed from the front,  end exit and collected from the open T fitting at the rear actuator.   I pushed fluid into the reservoir fill connection (with the overflow stopped off)  and  collected about 1/2 gallon  of clear hydraulic fluid with nowhere into a gallon jug.   I close the system and try to operate the flap pump lever,  but again it was inoperative and acted like there was air within the pump.   A year ago  I tried pushing fluid from the rear at the actuator forward and also was unable to fill the pump.  

 I spoke with Robert Brown (former manager Laser)  were rebuilt hydraulic flat pumps for Lasar when he was there.   He indicated to me that his last ditch  procedure was to remove the inbound hose at the flap pump and fill the front 1/2 of the hydraulic system  starting at the pump forward.   I  had already made a hose which I could attach to my pressure pot  which allowed me to to connect to  the pump end of that hose.   It was quite simple  to disconnect the hose,  some hydraulic fluid leaked out but I was able to quickly connect my pressure pot.   I pushed fluid forward collecting it  from the reservoir drain tube.   I collected about 1/2  of clear hydraulic fluid without air.   I  disconnected my pressure part from the inbound hose and quickly reconnected it to the flat pump.   After disconnecting everything  I tried the flap system by pumping the flap lever and the flats worked.  

 The retraction speed was off  but that is adjusted by a large and anteriorly located screw and locknut on the flap pump.    Turning the screw  counterclockwise increases the speed and turning the screw clockwise slows the speed.   The ideal goal is 12 seconds of retraction.   The screw is very sensitive  and after several tries I was jumping between 5-6 seconds and 12-24 seconds with just a turn of about 5-10 degrees.   After several tries,  holding the slotted screw  placed through a box wrench holding the locking nut,  I was able to adjust the screw and finally tighten the assembly without a problem.   I final retraction speed is 12 seconds.   The flap handle operation  is exactly 4 pumps to lock out  which is what is expected to occur.

 It seems that Robert Brown's procedure works.   I'm still not sure why pushing fluid from the front fails to prime the pump.   There are two one-way ball valves  which are oriented to allow fluid to pass from front to back,  but it has not worked  to prime the pump successfully.   Their are reports that you can push  hydraulic fluid from the rear actuator forward to the reservoir,  but in order to do that one needs to back off on the large adjustment screw creating a larger leak for the fluid to  flow through the pump and into the anterior part of the system.   I  believe that that would likely work and would bypass the problem of attempting to flow fluid against the two checkouts,  but I just didn't need to because opening the system in the middle and backfilling from the pump forward worked.   I think what I was doing as well is allowing the fluid placed in the anterior part of the system to prime the pump once reconnected.

 When adjusting  the speed and trying to get all the air out of the system,  I operated the flap handle placing the flaps down,  which draws fluid into the hydraulic pump from the front part of the system and pressurizes the rear part of the system causing the actuator to move.    With each adjustment,  I left the flaps  fully in the down position and just cracked open the at the actuator  so that it dripped hydraulic fluid.   There was no suggestion of error in the system.   Then I tightened AN  at the tee of the actuator.

 With the flaps still down,  I had hydraulic fluid to the reservoir with a pressure pot until I collected more than a pint of clear air free fluid.   I then disconnected fresh product closed system.   I repeated this procedure several times.

 The system now seems to be reliable and  operates consistently with 12 seconds of attraction and for palms to lockout.

The Mooney  manual information is not helpful  nor is it clearly written.

 Since I have now found a  procedure that works,  I think this will be my go to procedure in the future.   Using hoses  for connectivity and fittings at directly from pressure pot  and to collection jars,  at the end of the hose ideally submersed in an intro so of hydraulic fluid,  allows one to avoid the complete mess that is easily made with hydraulic fluid leaking everywhere and floor.

 Hope this is helpful.

John Breda

 

[M20F-1968]

Of course, work was done with my A&P/IA's supervision.  We just wanted to post the procedure as it is not documented anywhere, and the typical procedures that are written has been ineffective more than not.

John Breda

[MB65E]

To get it to prime from the front there needs to be differential pressure and a leak at the same time. I went round and circles this summer. I was surprised it bled with the cap off at the rear and pumping the handle. With the rear cap on there is no differential pressure to displace the air in the line. But I didn’t understand how it could hold fluid with the line wide open. 
Glad you found what works. 
-Matt 

[N201MKTurbo]

I have found that if you remove the fitting on the actuator and have someone pump the flap pump. You take your finger off the end of the hose while they pump down and then put your finger on the hose while they pull the handle up, this eventually gets fluid flowing. When that is working, reconnect the hose to the actuator and have them pump it up, then loosen the hose on the actuator and let the flaps come back down. This will push any air in the actuator out. You may want to do this a few times. It makes a big mess and you will get a bit of dermatitis from having your hands covered with 5606 for a while. Gloves don't help they just get full of fluid and make it worse.

[M20F-1968]

Using Dragon Software is many times not the best.  The corrected version is:

I changed out my hydraulic flap pump  about a year ago but it was not acting correctly.   The first  pump of the day was ineffective,  then it acted normally for the rest of the day with four pumps to lock-out as it should be.   However,  after several days of sitting the problem reoccurred.

 I had my belly pan off recently and decided to readdress this issue.   I tried  attach  a pressure pot to the aft end of the system by removing the cap on the T fitting and pushing hydraulic fluid forward.   With this  procedure alone the system became unresponsive and there was clearly air in the flap pump.

 I went back to the manuals,  reviewed what I had done in the past,  and decided to make connection hoses so that I had options pushing hydraulic fluid from the front to the back,  as well as the back to the front.   These consisted of appropriate hoses  to the various AN fittings.   I also installed a pressure gauge onto my pressure pot.   The Mooney  suggests pushing fluid in the 30 to 40 psi range.

The manual states  that fluid should be pushed from the front,  and exit from the open T fitting at the rear actuator.   I pushed fluid into the reservoir fill connection (with the overflow stopped off)  and  collected about 1/2 gallon  of clear hydraulic fluid with no air into a gallon glass jug.   I closed the system and tried to operate the flap pump lever,  but it was inoperative again and acted like there was air within the pump.   A year ago  I tried pushing fluid from the rear at the actuator forward and also was unable to fill (prime) the pump.  

 I spoke with Robert Brown (former manager Laser)  who rebuilt hydraulic flat pumps when he was at Lasar.   He indicated to me that his last ditch  procedure was to remove the inbound hose at the flap pump filling the front 1/2 of the hydraulic system, in a retrograde fashion starting at the pump.   I  had already made a hose which I could attach to my pressure pot  and which allowed me to to connect to the pump end of the inbound hose to the pump.   It was quite simple  to disconnect the hose,  some hydraulic fluid leaked out but I was able to quickly connect my pressure pot.   I pushed fluid forward collecting it  from the reservoir drain tube.   I collected about 1/2  of clear hydraulic fluid without air.   I  disconnected my pressure pot from the inbound hose and quickly reconnected the inbound hose it to the flap pump.  I tried the flap system by pumping the flap lever and the flaps worked.  

 The retraction speed was off  but that is adjusted by the large, anteriorly located screw and locknut on the flap pump.    Turning the screw  counterclockwise increases the speed and turning the screw clockwise slows the speed.   The screw end is directed as at an aluminum seat and turning the screw creates a calibrated leak (separate from the inflow and outflow ball bearing/spring loaded check valves) returning fluid back to the anterior part os the system.  Lifting up on the Flap Handle in the cockpit moves fluid into the hydraulic chamber in the pump, and pushing down on the handle pressurizes the rear hose to the rear actuator..

The ideal goal is 12 seconds of retraction.   The screw is very sensitive  and after several tries I was jumping between 5-6 seconds and 12-24 seconds with just a turn of about 5-10 degrees.   After several tries,  holding the slotted screw  placed through a box wrench holding the locking nut,  I was able to adjust the screw and finally tighten the assembly without a problem.   My final retraction speed is 12 seconds.   The flap handle operation  is exactly 4 pumps to lock-out  which is what is expected to occur.

It seems that Robert Brown's procedure works.   I'm still not sure why pushing fluid from the front fails to prime the pump.   There are two one-way ball valves  which are oriented to allow fluid to pass from front to back,  but it has not worked  to prime the pump successfully.   Their are reports that you can push  hydraulic fluid from the rear actuator forward to the reservoir,  but in order to do that one needs to back off on the large adjustment screw creating a larger leak for the fluid to  flow through the pump and into the anterior part of the system.   I  believe that that would likely work and would bypass the problem of attempting to flow fluid against the two check valves,  but I just didn't need to try that because opening the system in the middle and backfilling from the pump forward worked.   I think what I was doing by this method allowed the fluid placed in the anterior part of the system to prime the pump once reconnected.  I do not yet understand why 35 psi did not prime the pump but gravity filling from the anterior hose did.

 When adjusting  the speed and trying to get all the air out of the system,  I operated the flap handle placing the flaps down,  which draws fluid into the hydraulic pump from the front part of the system and pressurizes the rear part of the system causing the actuator to move.    With each adjustment,  I left the flaps  fully in the down position and just cracked open the at the actuator  so that it dripped hydraulic fluid.   There was no suggestion of air in the system.   Then I tightened the AN cover on the tee at the actuator.

 With the flaps still down,  I added more hydraulic fluid to the reservoir with the pressure pot until I collected more than a pint of clear air free fluid from the overflow tube.   I then disconnected my pressure pot and closed the system (operating configuration).   I cycled the flaps and then I repeated this procedure several times.

 The system now seems to be reliable and  operates consistently with 12 seconds of retraction and for four pumps to lock-out.

The Mooney  manual information is not helpful  nor is it clearly written.

Since this procedure works,  I think this will be my go to procedure in the future.   Using hoses  with hard connections and fittings from pressure pot and drain hoses with appropriate fitting to collect fluid into collection jars cuts down on the mess immensely.  The open ends of the hose should be ideally submersed in an inch or so of hydraulic fluid so it will not accidentally suck air into the system.  

It took some time to sort though the details of how the system works.  Whatever you do, make sure the reservoir remains full as it does not hold that much fluid. 

The brake lines come off of the reservoir at a lower height, so you will loose flaps before loosing  brakes should there be a leak in the system and the reservoir fluid level is low.  Make sure the reservoir remains full.  I understand full means different things depending upon your reservoir type.

The work was done with the supervision of an A&P/IA.

 Hope this is helpful.

John Breda