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.