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
www.N91CZ.net