Wolfgng,
“How do
some spools come off their endpoints and cause reported failure?”
That
question was answered long ago. I
can show you how to rig a pump to lock up and then I can show you how to rig
it such that it can’t lock up.
Developing a fix for a problem before understanding the root
cause is not a smart way to go about things. You saw an issue on one airplane.
Unfortunately you refused to pull the pump to look at it, simply telling us
that the pump was too difficult to reach. That is a really poor excuse. Yes, the pump was behind the baggage
bulkhead and it is not easy to get to it. How can that be a valid reason for not
examining the actual hardware?
Initially
it was claimed this module would solve lock-up in both directions. Reading through the description of its
theory of operation, it is clear the module cannot catch the ‘failure to
extend’ lock-up. A system state
was missed.
There are
downsides to having to use the pump to forcibly unlock a thermally locked
system. I am sure you are aware
of those. I am curious what new
failure modes have been introduced if any one part of the module
fails?
I offered
to look at Lorn’s pump as I have done for others. Your reply was that a week or two of
down time was too much of a price to pay. Really!
I am
still in search of a pump that falls outside the expected behavior when
configured properly. I would
truly like to find one as it can only serve to further our understanding of
our planes. What a shame and loss
to the community if you (or really Lorn) truly possess such a pump. I know, I know, it is too much effort
to pull the pump.
Please
don’t extrapolate the behavior of the one pump you saw only from the outside
to the rest of the fleet.
Disclaimer: I don’t
have a financial interest in this discussion…….well maybe I do. I am trying to keep our insurance
rates from going up.
For your
entertainment I have attached some photos of my pressure gauges after my plane
was exposed to thermal soak, both in the air and on the ground. You will see that only the commanded
side is affected by thermal influence.
And here
are some video clips:
The first
video shows how a pump with spool return springs can lock up when subjected to
rising temperatures. The second
clip shows a pump without return springs. Only the currently active side is
affected by temperature changes.
No lock-up
Chris
Zavatson
N91CZ
L360std
1,400 hrs (lock-up free)
www.N91CZ.net
From: Wolfgang
<Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Thursday, February 14, 2013 11:48
AM
Subject: [LML] Re: Fw:
[LML] Re: Thermal influence on Hydraulic Pressure
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.