This is for the aficionados of old hydraulic pumps.  Mine is from 1989 and I’m having trouble with the retract cycle.  Since my post several months ago I have installed pressure gauges, rebuilt the nose leg actuator, sequence valve and gear door actuator, and serviced the pump with the kit from Lancair.  Same problems, but at least the pressure gauges help diagnose.

 

On the retract cycle pressure builds up on the low side as well as the high side and the pump stops until the low side pressure drops, the pump restarts, raises the gear a bit further, stops, and so on.  Once the gear is up, the pressure on the low side drops off and high side pressure is maintained.  These are symptoms of a reversed spool valve, but this pump’s is symmetrical with a single o-ring.

 

Lowering is OK, and pressure is maintained in the down and locked position, so apparently no internal leaks. 

 

I guessed the return line was blocked, or the ball valve sticky.  See the attached photos.  The spring is very stiff and takes about 15 lb to close it about 0.1 inches.  With a port diameter of less than 1/10 inch, this translates into about 2000 psi to overcome that force.  This doesn’t look like it’s offering only 100 psi resistance and it seems  beefier than the example on Chris Zavatson’s figure 14 on N91cz.com...  Can anyone confirm that the spring looks right or wrong—maybe Friday afternoon at the factory?  And where can I get a replacement return line spring and ball? 

 

The photo of the pump shows the return valve location on the left. 

 

Thanks in advance.

 

Regards, Chris.