The dump valves in the 360/320 did not "dump" to
the reservoir, it only cross connected the high and low sides of the hydraulic
pump. But you know that.
Changing it out for a valve the that does
"dump" to the reservoir was one of my suggestions quite a while back since the
pump body already has ports to accommodate that.
Again, forced running of the pump in the
appropriate direction (determined by the gear switch position) when both hi
and lo pressure switches have been tripped rendering the pump inoperable, WILL
clear the problem. That's what a pressure switch monitoring module does,
automatically. This solution works for the 320, 360 and
Legacy.
This solution does not rely on the pump behaving
as it should for the service life of the pump. I like more than one way of
preventing potential hull damage.
This solution can also be implemented by a manual
push button switch on the panel but requires pilot
intervention.
"if condition are just right, shut the pump down"
. . . but once the pulse subsides (miliseconds)
that event is over because the un-extended gear down cylinder volume will
absorb that pulse.
. . . unless there is a blockage in the lines . .
. then you have other problems.
There is no need to theorize the problem into
obscurity. KISS principal rules.
Wolfgang
----- Original Message -----
Sent: Tuesday, April 22, 2014 7:59
AM
Subject: Gear Down...INOP
Hitting the
dump valve may or may not help the problem.
It depends on how much of a
temperature increase you incurred.
Wolfgang
============================================
Wolfgang,
I suggest a review of the Legacy hydraulic
system schematic in the following document (Legacy Addendum).
http://www.n91cz.net/Hydraulics/Lancair%20Hydraulics.pdfYou will see that
the Legacy has a three-way dump valve that connects both high and low sides to
the reservoir. It will always dump pressure regardless of temperature
rise.
Extension
failures were more common in the 320/360 and can be resolved by simply
adjusting the low side pressure switch higher (and if needed, the relief valve
also) -see page 10. The higher volume gear pump in the Legacies reduces
the exposure to the failure when using stock pressure settings.
The initial extension sends a
pressure pulse through the system and can, if condition are just right, shut
the pump down. The hydraulic system will think the gear is down and
pressurized. This type of failure is what caught Lorn off-guard and
resulted in a gear-up landing. See attached, the photo of Lorn�s pressure
gauges after he slid to a stop. Both gauges are 500 psi +/-.
The gear selector is down, the
low side pressure switch is open and the high side pressure switch is
closed. The very same condition as when the gear is fully down and
locked. Based on prior descriptions of your module, it will not detect
this condition as a failure and will do nothing to fix it.
Most Legacy pumps
have spool return springs which can cause pressure rise in both sides due to a
temperature increase. This is more often an issue sitting on the
ground on a hot parking ramp where the potential temperature swing is
much greater. I recommend removing these springs per instructions in
this link:
Chris
Zavatson
N91CZ
360std