Randy, Lorn, Scott, et al,

One of the issues raised was the trapping of pressure in the down side circuit with the gear in the up position.  In the current pump configurations (?? at least back to 1995, probably much longer),  the back pressure circuit opens up a low resistance path back to the reservoir.  Without it, the low side can rise to the setting of the relief valve during retraction, leaks from the high side, thermal expansion, etc.  Again, we appear to have some older configurations that may behave differently, however, trapping pressure on the low side up to its operating operating is exactly what the back pressure circuit is supposed to prevent (assumes the spool valve is in the correct orientation, of course).

 

The following link is to a video of an intentional leak from the high to low sides, with the system pressurized in the up direction.  I used a leaking dump valve (removed from my plane several years ago) as my leak source.  To accelerate the leak for purposes of taping, I just barely cracked the valve.  You'll see the movement in the high side pressure gauge as the pressure rises and falls.  Pressure never builds in the low side.  All fluid is returned to the reservoir.

 

 

This second video is sort of a follow on the one above.  I used a shutoff valve to isolate the low side of the test subject - the faulty dump valve - from the return side of the pump.  In that way I can charge the high side, then open the test valve and  let the pressure start to build on the low side of the test valve.  I continue this cycle until I have about 1000 psi on each side of the faulty dump valve.  Now I reconnect the return line to the pump.  The low side immediately dumps back to the reservoir.  No pressure is maintained in the low side circuit.

 

 

Chris

 

 

 

 

 

 

Chris Zavatson

N91CZ

360std.