Bob,

One of the tests I recorded this weekend was for the scenario of pushing the gear up by hand with the spool valve in the down position.  It is becoming clear through this hydraulics thread that there exit some internal differences between the early pumps and current models.

 

In this video, I extend a single cylinder on the test bench.  The test bench is set up just like the aircraft system.  After "extending the gear" I turn off power to the pump and open the dump valve.  Next I try to retract the cylinder by hand.  You can see the pressure build in both sides of the cylinder.  Since the spool valve is still in the "down" position, the back pressure circuit is not active.  Attempting to push the rod volume into the fluid system produces the pressure seen on the gauges.  Once I bump the pump in the up direction and the spool valve slide over to the "up" posistion, I can push the rod all the way in without pressure build up.

Again, this behavior only applies to the most recent configuration.

 

Here is a link.

Chris

 

 

 

 

Chris Zavatson

N91CZ

360std.