Larry,

 

Just to review: 

 

When the gear is up and the current dump valve is opened, there is a tremendous need to route up fluid to the down side for a second or two.  This is because of the spring loaded door actuators and especially for the nose gear actuator since the gas spring is exerting an immediate force.  The dump valve is located near the nose actuator and initially the fluid in the up side of the actuator is short circuited to the down side thru the valve.  Eventually, demands are made on the pump reservoir because the down side uses more fluid than the up side (the push rods are outside the chamber when the gear is extended).  It is unlikely that the gear would not come down even if initially the pressure had the shuttle valve in the wrong position since the demand to move fluid is so great.  There is no problem with this high priority function of the current dump valve regardless of the pressure switch conditions.

 

When the gear is down and system pressure builds on both sides (up and down, for any reason) such that the pressure switches are both open and the shuttle valve is mis-positioned so that no relief is given on either line.  The pump is not started on a request for gear up, so then the dump valve is opened and there is no change because there is no external force being applied to the gear system (all down and locked) and the pressure differential is not great enough to drop the up side switch pressure enough to close the contacts.  Consider that the dead band (the pressure range for which the switch remains open) of both switches overlap.  That is, the lower limit range of the up pressure switch is low enough so that the switch is opened by pressure built up in the system and even the down side won't energize the pump.  Also, the switch mechanism may also be sluggish or the switch contacts may be a bit burned or corroded (no MOV or diode in the relay coil circuit) and that may indirectly affect the pressure range for closing the switch.

 

One solution to the latter problem is the 3-position dump valve (off, dump, and up side pressure relief back to the reservoir).  Such a solution is messy since the replacement of the dump valve is problematic for those of us that have full radio stacks.  The high pressure line could be tapped for a separate valve in some location that would be more friendly.  This valve could be opened and closed as part of every pre-flight check-list.

 

Although this solution resolves the odd occurrence of the pressure problem, it does not address an issue of a failed pressure switch.  While a wee Lancair can fly with the gear extended, the 122 KIAS limitation is, uh, a limitation.  That is why I suggest a hidden momentary push button switch to bypass the pressure switch for those that regularly experience the problem. Once the pump starts, things should improve.  BTW, I do have an accessible bypass switch for the air pressure driven squat switch (also useful on jack stands when doing gear tests).  For me, wiring is easier than plumbing.

 

Larry, if you want to whup Mark, consider Randy's install of the ECI cold air intake system. 

 

Grayhawk

 

 

The dump line goes to the tank and ends submerged in fluid with a ¼” down tube in the reservoir.  Additionally, in my opinion no fluid would ever travel upstream toward the valve.  Thus, no air would be added to the system by use of a 3 way vavle.