Hydraulic flap pump aggravations

[M20F-1968]

I recently decided to R & R my slightly leaking flap pump.  Installed the new pump and followed in instructions I was given from a good source which called for bleeding the system from the inflow line to the pump first forward to the reservoir overflow.  Then there is a burping process when the line remains submerged in 5606 and the line is temporarily blocked by a finger, emitting small bubbles when released.  Once no more air is seen, reattaching the line, pump down the flaps, and cycled the flaps, bleeding each round from the actuator.

This all worked predictable and the flaps worked well.  However, I had a gravity fill line up front which did not work and I emptied the reservoir.  I thought I was almost doe when mid- fourth flap cycle the handle went limp and feels like it is pumping air.  The question is, do I now need to bleed differently given that it seems there is air in the pump?  It has been suggested that some dirt is holding one of the little balls open.  What is the quickest way to troubleshoot this problem?

Some have suggested that I bleed from the actuator clear to the reservoir.

John Breda

[carusoam]

Inviting the flap pump whisperer to the conversation... @Shadrach...

Ross Has sooooo many skills.... but few have real knowledge of the flap pump...

Best regards,

-a-

[Shadrach]

23 minutes ago, M20F-1968 said:

Some have suggested that I bleed from the actuator clear to the reservoir.

John Breda

In my experience this method yields the most consistent results. This is not to say that others won’t work.

What is the symptom behind the “dirty little balls”  theory? Bleeding issues typically manifest differently than mechanical/valve issues.

[Nukemzzz]

Sounds like you sucked air from the reservoir and just need to bleed again. To bleed the pump I had to disconnect the shaft and fully actuate it to the bottom and top  of the stroke as the handle won’t do this. 

[M20F-1968]

I got the system working.  Yes, I sucked air in from the reservoir.   

In order to clear the problem I had to split the system in the middle.  I hooked up a pressure pot to the feed line into the hydraulic flap pump and bled the line to the front through the overflow line from the reservoir.  I put a clear line onto the outflow and submersed the open end in hydraulic fluid.  Then, with a finger, momentarily stopped the line, then opened it with the line submerged to get additional air out under pressure.  The pressure pot was disconnected to the front half of the system and the line capped at the pump. 

Then I connected to the inflow fitting on the pump to the pressure pot and pushed hydraulic fluid from the inflow fitting , through the pump, and into the rear actuator.  It took several hours to cycle the flaps, by initially lowering them, and raising them by cracking the cap at the rear actuator to raise them, all the while keeping the pressure pot connected to the inflow (larger) fitting on the flap pump.   This was done probably 20 times to insure the pump and rear 1/2 of the system was full and air free.  One needs to ensure pressure is maintained at the pressure pot to keep the system supplied with fluid.  When the line showed clear consistent fluid leakage (with the rear cap cracked open), the rear actuator cap was closed, and the inflow line (forward 1/2 of the system) was connected to the pump.  

Then, it took several hours to cycle the flaps again in the same manner, except that the system was filled through the system by the reservoir.  One needs to keep the reservoir filled after each cycling of the flaps.  Flaps were initially lowered, and raised them by cracking the cap at the rear actuator.  This was done probably 20 times.  

Then the timing for flap retraction was adjusted by the large screw on the forward aspect of the pump.  Clockwise to slow flap retraction and counterclockwise to quicken flap retraction.  With each reconfiguration, the system needs to be re-bled and reconfigured.  The flap cable needs to be rigged. It moves less than 1/4 of of a circle, and needs to bridge the zone of flaps up and flaps down.  Start with the cabin handle up and the flap pump lever at 6:00 o'clock.

John Breda