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What did you measure to come up with that 70 g's
?
and . . . the springs trying to center the spool in
some models certainly don't help.
So the question still lingers from more than a year
ago,
How do some spools come off their end position and
cause the reported failures ?
That's why I came up with the module I have.
It powers the spool back into position whenever
needed, regardless of pump model.
Wolfgang
----- Original Message -----
Sent: Wednesday, February 13, 2013 7:55
AM
Subject: Re: [LML] Fw: [LML] Re: Thermal
influence on Hydraulic Pressure
Reposted from June 2011
=============================================================
-----
Original Message -----
Sent:
Saturday, June 25, 2011 12:35 PM
Subject:
Re: [LML] Re: LNC2 Gear Hydraulics
Curiosity got the best of me. Here are the peak vibration values
recorded today at the hydraulic pump measured on the axis of the
spool valve.
Start up: +/- 1.3 g
Take off: +/- 0.3 g
Cruise: +/- 0.1 g
Descent: +/- 0.1 g
Landing: +/- 0.6 g
It would appear the O-ring has more design margin than just about
any other component on the
plane.
Chris Zavatson
N91CZ
360std
==============================================================
From: Wolfgang
<Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Monday, February 11, 2013 12:36
PM
Subject: [LML] Fw: [LML]
Re: Thermal influence on Hydraulic Pressure
70 g's is an impressive number. How was that
measured ?
Or is that just a measure of the vibration
that the part lives under during flight ?
Wolfgang
From: Chris Zavatson
<chris_zavatson@yahoo.com>
To: lml@lancaironline.net
Sent: Saturday, January 26, 2013 12:24
PM
Subject: [LML] Re: Thermal
influence on Hydraulic Pressure
Randy,
Thanks.
There
are two things I have been doing to pumps to eliminate the need for 'dump
valve rescues'.
First is the removal of the return springs that entered the Legacy
pump design in about 2005. They added no useful functionality
and unfortunately introduced a lock-up failure mode. Removing the
springs primarily addresses lock-up on the ground during thermal
swings.
The second thing I have been doing is to set the low pressure
switch to 800-850 psi. This eliminates the gear extension lock-up mode
that occasionally prevents
the gear from fully extending. The original setting was to low to
overcome the pressure spike that propagates through the system
when the gear first come out of the wheel wells.
The
other thing I have been doing is measuring the spool resistance on every
pump that comes across my desk. I haven't found any issues there.
70g's is the
typical result.
I have also been making thermal relief valves adjustable, bringing
the set-point into a usable range (2,000 psi) for our systems.
The
three-way dump valve references in that write-up were merely
describing the Legacy hydraulic system. The Legacy cannot
perform a gear free-fall extension without a three way valve due to
cylinder orientation. I still use a two-way valve in my
360.
Chris
Chris Zavatson
N91CZ
360std 1,400 hrs
http://www.n91cz.net/
From:
randy snarr
<randylsnarr@yahoo.com>
To: lml@lancaironline.net
Sent: Friday, January 25, 2013 5:23
AM
Subject: [LML] Re: Thermal
influence on Hydraulic Pressure
Nice Work Chris..
I
am happy to hear that I have already done what you suggested which is to
install a 3 way dump valve and run the dump line to the reservoir in a low
pressure line. It has worked very well. I dont like having to open the dump valve but it
is necessary once in a while especially when it is cold. The pressures on both
sides of the system climb due to the engine heat and the gear sometimes will
not move without dumping the pressure.
Have you found
a solution for this with your research that makes the original system function
without having to ever dump the pressure manually?
Randy
Snarr
235/320
N694RS
"Flight by machines heavier than air is
unpractical and insignificant, if not utterly impossible"
-Simon
Newcomb,
1902
From:
Chris Zavatson <chris_zavatson@yahoo.com>
To: lml@lancaironline.net
Sent: Tuesday, September 4, 2012 2:18
PM
Subject: [LML] Re: Thermal
influence on Hydraulic Pressure
Danny,
No affect on gear
movement.
I should add however that
elevated high-side pressure is one of the contributing factors to gear
extension failures in a standard system set up. My low pressure setting is
higher than the nominal 550 psi. It is set to 800 psi to avoid the
pressure spike that propogates through the system when gear down is
selected.
see "Failure to Extend" on page
10 for more detail.
http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf
Chris
Zavatson
N91CZ
360std
From: Danny
<danny@n107sd.com>
To:
lml@lancaironline.net
Sent:
Monday, September 3, 2012 11:54 AM
Subject: [LML] Re: Thermal influence on
Hydraulic Pressure
Chris,
What was the impact on the gear
movement?
Danny
LNC2-360
N
38° 43' 25.7"
W
77° 30' 38.6"
From: Chris Zavatson
[mailto:chris_zavatson@yahoo.com]
Sent: Saturday, September 01, 2012 11:32
PM
To:
lml@lancaironline.net
Subject: [LML] Thermal influence on
Hydraulic Pressure
-took
this photo after a descent from 16.5k to 1,500
ft.
OAT went
from 42 to 94 degrees.
High
Pressure gauge is pegged at 2,000+ psi
-Didn't
get a photo, but the opposite happened on the ramp in Spokane. After
sitting for an hour, the low pressure gauge was pegged at 1,200 psi+.
Spokane might not be the warmest spot in the country, but at 85 deg F, it was
55 degrees warmer than the cold soak on the previous
leg.
Temperature
changes have a big impact on system pressure.
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