----- Original Message -----

From:
willydford [at] gmail.com" href="mailto:willydford [at] gmail.com" rel="noopener" target="_blank">William
Ford

To: lml [at] lancaironline.net

Sent: Wednesday, April 16, 2014 10:06
AM

Subject: Gear Down...INOP

I believe that I recently experienced something in my Legacy that
I remember reading about but can't remember all the details.  I looked
into the LML archives and was unsuccessful.  Could someone out there
please briefly summarize the situation, reason and any possible remedies for
gear extension failure following high altitude cruise in cold air followed by
a decent and landing in hot air.  I seem to remember a discussion about
boosted pressure in the hydraulics plumbing due to the rapid rise in
temperature which in turn had an effect on the operation of the pressure
switch  In my recent experience...after opening the dump valve, the
hydraulic pump did run, confirming continuity to the pump.  After working
the nose gear into the locked position, the landing was uneventful but I would
like to avoid this uncomfortable situation in the future.  Would a tweak
on the pressure switch adjustment be called for here or just expect to
momentarily crack open the dump valve to relieve excess pressure.  Thanks
for your thoughts.

William Ford

N11LL

Hitting the dump valve may or may not help the problem.

It depends on how much of a temperature increase you incurred.



Wolfgang



----- Original Message ----- From: "Kevin Stallard" <kevin [at] arilabs.net>

To: <lml [at] lancaironline.net>

Sent: Monday, April 21, 2014 11:43 AM

Subject: RE: [LML] Gear Down...INOP





Do you have hydraulic pressure gauges installed so you can see the pressure on the high and low side?



I suspect that quickly opening and closing the dump valve would cure your problems, because yes, there is an interaction that occurs between the high and low side and the poppet valve in your pump.   But unless you know the pressure on the high and low side when the problem occurs, I can't say for sure.



I've seen this once on my plane.  Hitting the dump valve quickly solved the problem.



Kevin



________________________________________

From: Lancair Mailing List [lml [at] lancaironline.net] On Behalf Of William Ford [willydford [at] gmail.com]

Sent: Wednesday, April 16, 2014 8:06 AM

To: lml [at] lancaironline.net

Subject: [LML] Gear Down...INOP



I believe that I recently experienced something in my Legacy that I remember reading about but can't remember all the details.  I looked into the LML archives and was unsuccessful.  Could someone out there please briefly summarize the situation, reason and any possible remedies for gear extension failure following high altitude cruise in cold air followed by a decent and landing in hot air. I seem to remember a discussion about boosted pressure in the hydraulics plumbing due to the rapid rise in temperature which in turn had an effect on the operation of the pressure switch  In my recent experience...after opening the dump valve, the hydraulic pump did run, confirming continuity to the pump.  After working the nose gear into the locked position, the landing was uneventful but I would like to avoid this uncomfortable situation in the future.  Would a tweak on the pressure switch adjustment be called for here or just expect to momentarily crack open the dump valve to relieve excess pressure.  Thanks for your thoughts.



William Ford

N11LL

I believe that I recently experienced something in my Legacy that I remember reading about but can't remember all the details.  I looked into the LML archives and was unsuccessful.  Could someone out there please briefly summarize the situation, reason and any possible remedies for gear extension failure following high altitude cruise in cold air followed by a decent and landing in hot air.  I seem to remember a discussion about boosted pressure in the hydraulics plumbing due to the rapid rise in temperature which in turn had an effect on the operation of the pressure switch  In my recent experience...after opening the dump valve, the hydraulic pump did run, confirming continuity to the pump.  After working the nose gear into the locked position, the landing was uneventful but I would like to avoid this uncomfortable situation in the future.  Would a tweak on the pressure switch adjustment be called for here or just expect to momentarily crack open the dump valve to relieve excess pressure.  Thanks for your thoughts.



 

Attachment: Gear Up Pressure Gauges.jpg 

(130K)

<< below

Chris,

 

I remain unconvinced with your theory. You have
suggested that the pump will somehow shut down immediately after it has started
up due to some pressure pulse. The mechanisim of which you have yet to clarify,
let alone demonstrated.

 

I'm tired of your kibitzing and since you have
proven that you can't let it go, I will and leave you to humor
yourself.

 

Wolfgang

 

----- Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank">Chris
Zavatson

To: lml [at] lancaironline.net

Sent: Saturday, April 26, 2014 1:28
PM

Subject: Gear Down...INOP

Wolfgang,

<<“I
believe in redundancy and it looks like you
don't….”>>

I
am a big proponent of redundancy. 
That is redundancy defined as a true back-up to an otherwise
trouble-free system.

First, I have redundant switches to power the pump solenoids.  This allows me to raise and lower the
gear in case of the failure of either of the pressure switches.  It doesn’t happen very often, but it
does happen - twice in 17 years of flying my 360. 

I
also have redundant gear down indications.  Two completely separate systems,
separate switches, separate wires and separate indicators.  The second set of switches is mounted
directly on the over-center links.

I
even carry two iPads and a iPhone - just in case

<<“The
pressure pulse you're talking about will subside (glad you agree) and as it
does, because the cylinder is only partially extended, the cylinder will
continues to extend, the low switch will close again, and enable the pump to
continue . .”>>

The
part you seem to be missing here is that the momentary pulse is not directly
turning off the pump.  Thus when
the pulse subsides, the pump doesn’t just spring back to life.  The pulse pushes the spool in the
wrong direction -against the pump flow. 
This locks the poppet that the pump just opened up a fraction of a
second earlier.  When this
happens, the high side begins to pressurize along with the low side.  As soon as both sides reach the low
side pressure setting, the pump is turned off.  This is why you see both high and low
circuits pressurized to the same value in Lorn’s photo.

To
prevent this, the low side pressure settings should be raised.  800 psi has proven sufficient.  The high volume gear pump will reduce
the size of the pulse since the higher volume pump is able to absorb incoming
fluid at a higher rate.

I
highly recommend pressure gauges for both high and low circuit be installed in
a location visible to the pilot. 
The state of the system can always be verified.  One can immediately diagnose any
in-flight problem.  Leaks can be
caught early.  And adjusting
pressure settings is no longer guess work.

Chris
Zavatson

N91CZ

360std

www.N91CZ.net

I have also worked with Chris on several items on my project for the past years.  He is honest, diligent and his research skills are exemplary.  As Kevin mentions, he strives to find the correct answer through his research and discussions with other pilots.

There is no need to malign people on this list.



Doug



-----Original Message-----

From: Lancair Mailing List [lml [at] lancaironline.net (mailto:)

] On Behalf Of Kevin Stallard

Sent: April-28-14 9:10 AM

To: lml [at] lancaironline.net

Subject: [LML] Re: Gear Down...INOP



Wolfgang,



I am surprised that you remain unconvinced.  Chris' analysis on this topic has been the most thorough and careful analysis I've encountered.  He doesn't just look at the outside symptoms of the problem, but also delves into aspects of the pump and its design (the number of different configurations and variations available) that I never even considered previously.



I thought it was just a pump, I had no idea that the inner workings had such an impact on how the system operated until he took the time to take me through it all.  



I have had the opportunity to work directly with Chris in a professional setting, I have not encountered a more keen understanding of how things work and what questions to ask when things go wrong than that of Mr. Zavatson.  He has been able to point out errors in my thinking and how I look at problems in a way that has been very beneficial to me.  



These remarks that you have directed to him concern me greatly.  You aren't asking any questions, you aren't having a discussion, you aren't trying to reconcile the deficit of your understanding of these things, you are attacking him personally.  That's where you are losing me.



I'm starting to believe that the  results of someone following your advice and using your system could have dangerous if not life threatening consequences.  



I think what I would like to see from you is a bit more effort to reconcile your the observations Chris has replicated numerous times on the bench and in the air.  This is what I'm used to seeing when good willed scientists and engineers disagree.



I have observed Chris quickly change course if evidence is presented that refutes his conclusions.  He is not concerned with being right, he is concerned with what is right, constantly rechecking and questioning his own results..  I think you are a very smart and capable individual and we would all benefit if you adopted these same principles.



Thank you,

Kevin Stallard

N969RJ  150 hrs and counting!

________________________________________

From: Lancair Mailing List [lml [at] lancaironline.net] On Behalf Of Wolfgang [Wolfgang [at] MiCom.net]

Sent: Monday, April 28, 2014 5:59 AM

To: lml [at] lancaironline.net

Subject: [LML] Re: Gear Down...INOP



Chris,



I remain unconvinced with your theory. You have suggested that the pump will somehow shut down immediately after it has started up due to some pressure pulse. The mechanisim of which you have yet to clarify, let alone demonstrated.



I'm tired of your kibitzing and since you have proven that you can't let it go, I will and leave you to humor yourself.



Wolfgang



----- Original Message -----

From: Chris Zavatson<chris_zavatson [at] yahoo.com (mailto:)

>

To: lml [at] lancaironline.net<lml [at] lancaironline.net (mailto:)

>

Sent: Saturday, April 26, 2014 1:28 PM

Subject: Gear Down...INOP



Wolfgang,



<<"I believe in redundancy and it looks like you don't....">>



I am a big proponent of redundancy.  That is redundancy defined as a true back-up to an otherwise trouble-free system.



First, I have redundant switches to power the pump solenoids.  This allows me to raise and lower the gear in case of the failure of either of the pressure switches.  It doesn't happen very often, but it does happen - twice in 17 years of flying my 360.



I also have redundant gear down indications.  Two completely separate systems, separate switches, separate wires and separate indicators.  The second set of switches is mounted directly on the over-center links.



I even carry two iPads and a iPhone - just in case



<<"The pressure pulse you're talking about will subside (glad you agree) and as it does, because the cylinder is only partially extended, the cylinder will continues to extend, the low switch will close again, and enable the pump to continue . .">>



The part you seem to be missing here is that the momentary pulse is not directly turning off the pump.  Thus when the pulse subsides, the pump doesn't just spring back to life.  The pulse pushes the spool in the wrong direction -against the pump flow.  This locks the poppet that the pump just opened up a fraction of a second earlier.  When this happens, the high side begins to pressurize along with the low side.  As soon as both sides reach the low side pressure setting, the pump is turned off.  This is why you see both high and low circuits pressurized to the same value in Lorn's photo.



To prevent this, the low side pressure settings should be raised.  800 psi has proven sufficient.  The high volume gear pump will reduce the size of the pulse since the higher volume pump is able to absorb incoming fluid at a higher rate.



I highly recommend pressure gauges for both high and low circuit be installed in a location visible to the pilot.  The state of the system can always be verified.  One can immediately diagnose any in-flight problem.  Leaks can be caught early.  And adjusting pressure settings is no longer guess work.

Chris Zavatson

N91CZ

360std

www.N91CZ.net

--

For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html



----- Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank">Chris
Zavatson

Sent: Monday, May 05, 2014 7:14 AM

Subject: Re: [LML] Re: Gear
Down...INOP

Wolfgang,

The concept I have
trying to describe here and in my hydraulics write-up is nothing new.  It is however difficult, if not
impossible, to identify without instrumentation.  Most often this phenomenon simply
causes what is perceived as a hesitation during gear extension.  Sort of a quick Start-Stop-Start with
the gear continuing all the way down.  It becomes quite clear what is
happening if one looks at the system pressures when gear-down is
selected.  Analog gauges are best
for catching the interaction. 
What you�ll see is a pressure pulse just as the gear starts to
fall.  The magnitude of the pulse
is made greater by a few factors: 

1. Warm/hot hydraulic
   fluid (lower viscosity)
2. Outback gear (adds
   gear down force)
3. High-side pressure
   well above nominal (descending into significantly warmer air)
4. Original, lower volume
   gear pump

When the landing gear is in the
retracted position, it stores a lot of potential energy.  This is from the mass of the landing
gear, the pressure on the high side circuit and, with the outback gear, the
aero loads trying to pull the gear down.

It
is useful to look at Figures 9 and 10 in the hydraulics write-up when trying
understand the chain of events. 

http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf

In Figure 9,
you�ll see state of the pump while the gear is retracted.  When beginning the extension cycle,
the pump builds up pressure behind the spool (right side) and pushes it
against the poppet valve on the left as seen in Figure 10.  Opening the high side poppet valve
opens a path for fluid from the high side circuit to return back to the
pump.  It is not just the pump
moving fluid though.  All the
stored energy in the system is released and the falling gear, now also pushing
fluid back to the pump.  Given the
fixed volume nature of the gear pump, it can only absorb fluid at a certain
rate.  If the gear pushes the
fluid back faster than the pump can absorb it, back pressure builds up in the
high side circuit.  With enough
back pressure the spool is pushed back to the right.   As this happens, the high side
poppet starts to close off again. 
Pressure begins to rise and propagates backwards through the
system.  As soon as the low side
pressure rises above the pressure switch set point, the pump is shuts
down. 

Most of the time, the shut-down
is momentary.  This is because the
pump takes time to spool down and it is still moving fluid as it does so.  At the same time, the falling gear is
losing energy.  If the pressure
spike was small, the pump side will win, the spool will again open the poppet
all the way and the gear comes down. 
If the spike was large, the pump will remain off and you will see equal
pressure in the high and low side, just like in Lorn�s photo.  Pressure will be just above the
set-point of the low side pressure switch and the gear will be partially
extended.  Mitigation simply
involves raising the low side pressure set-point so that the pressure spike
can no longer affect the switch and pump.

I really don�t expect you to be
convinced.  I post these details
for the benefit everyone.

For many years
now, I have been publishing all kinds of reports, studies, diagrams,
maintenance guides and videos of Lancair systems is to promote a better
understanding and safe operation of the LNC2.  If I have made errors somewhere,
please point them out.  But don�t
just say it is wrong or that you don�t agree. Please provide some legitimate,
logical reasoning, some data or something that makes the point. 

To be honest, I found many of
your posts to be a bit worrisome. 
They left me with the impression you did not have a full understanding
of the pump operating environment or its operation.

For example, when
discussing spool movement, you claimed the pump could be subjected to 70 g�s.
 The actual environment is much
more benign.   Vibration
peaks are more on the order of 0.1 G�s. 
Below is a link to a vibration study that looks at airframe vibration
in different phases of flight. 
The study was done while looking into an engine isolator issue, but is
a useful environmental baseline for anything mounted to the structure.   

http://www.n91cz.net/Vibration/Vibration_Summary.pdf

Another example was a question
regarding the ball and spring in the return line.  You had asked what their purpose
was.  This would normally a very
legitimate question.  My concern
was that you had already designed a circuit to alter pump operation without
being aware of or understanding the function of all the internal parts.

Innovation is a good thing, but
on an aircraft the level of required due diligence is quite high.

Lorn�s pump
definitely had issues.  Mounting
the pump behind the baggage bulkhead is not ideal. It discourages good
maintenance practices, just as it did in this case.  Being unwilling to remove it from the
aircraft to investigate the internals because it was �so hard to get to�
simply makes it impossible to properly investigate a problem.  When I offered to examine the pump,
the response was that these airplanes were built to fly and two weeks of
down-time was too much of a burden. 
That was unfortunate.  Based on
Lorn�s description of the pumps behavior I strongly suspected the root
cause of its problems would have been immediately obvious upon
examination.  I have disassembled
more pumps that I can remember. 
All were made to operate normally once configured and adjusted
correctly. 

Chris Zavatson

N91CZ

360std

www.N91CZ.net

 

On Monday, April 28, 2014 4:59 AM,
Wolfgang <Wolfgang [at] MiCom.net> wrote:

Chris,

 

I remain unconvinced with your theory. You have
suggested that the pump will somehow shut down immediately after it has
started up due to some pressure pulse. The mechanisim of which you have yet to
clarify, let alone demonstrated.

 

I'm tired of your kibitzing and since you have
proven that you can't let it go, I will and leave you to humor
yourself.

 

Wolfgang

 

-----
Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank" ymailto="mailto:chris_zavatson [at] yahoo.com">Chris
Zavatson

To:
lml [at] lancaironline.net

Sent:
Saturday, April 26, 2014 1:28 PM

Subject:
Gear Down...INOP

Wolfgang,

<<�I
believe in redundancy and it looks like you
don't�.�>>

I
am a big proponent of redundancy.  That is redundancy
defined as a true back-up to an otherwise trouble-free
system.

First, I have redundant switches to power the pump
solenoids.  This allows me to raise and lower the gear in
case of the failure of either of the pressure switches. 
It doesn�t happen very often, but it does happen - twice in 17 years
of flying my 360. 

I
also have redundant gear down indications.  Two completely
separate systems, separate switches, separate wires and separate
indicators.  The second set of switches is mounted
directly on the over-center links.

I
even carry two iPads and a iPhone - just in case

<<�The
pressure pulse you're talking about will subside (glad you agree) and as it
does, because the cylinder is only partially extended, the cylinder
will continues to extend, the low switch will close again, and enable the
pump to continue . .�>>

The
part you seem to be missing here is that the momentary pulse is not directly
turning off the pump.  Thus when the pulse subsides, the
pump doesn�t just spring back to life.  The pulse pushes
the spool in the wrong direction -against the pump flow. 
This locks the poppet that the pump just opened up a fraction of a
second earlier.  When this happens, the high side begins
to pressurize along with the low side.  As soon as both
sides reach the low side pressure setting, the pump is turned
off.  This is why you see both high and low circuits
pressurized to the same value in Lorn�s photo.

To
prevent this, the low side pressure settings should be raised. 
800 psi has proven sufficient.  The high volume
gear pump will reduce the size of the pulse since the higher volume pump is
able to absorb incoming fluid at a higher rate.

I
highly recommend pressure gauges for both high and low circuit be installed
in a location visible to the pilot.  The state of the
system can always be verified.  One can immediately
diagnose any in-flight problem.  Leaks can be caught
early.  And adjusting pressure settings is no longer guess
work.

Chris
Zavatson

N91CZ

360std

www.N91CZ.net



----- Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank">Chris
Zavatson

Sent: Friday, May 09, 2014 7:54 AM

Subject: Re: [LML] Re: Gear
Down...INOP

Wolfgang,

I believe the exact words were:

“I see
the centering springs but what about the added spring, eyelet and ball? Where
does that fit into the schematic?””

And

“Still,
that port with the added spring, I believe it's a return port for excess
hydraulic fluid that can be used with a three port dump
valve.

. . . but why the spring if it's plugged
anyway?”

I interpreted that to mean you did not understand the
purpose of the ball and spring and were unsure of the purpose of the third
port that houses them.  Please
correct me if I misunderstood your questions.

I support only logic.  I base my statements on repeatable,
demonstrated facts and sound logic. 
I then apply them to reported observations to help explain anomalies
and trouble shoot systems.  I am
quite willing to discuss any aspects of hydraulics with you, but no technical
counter arguments have been forthcoming.

Without intending any disrespect, observations in the
absence of key data can easily lead to incorrect hypotheses.  For example, the early theories about
how pressure would migrate from the high side to the low side “due to low
temperatures”; or assuming the state of pressure switches without actually
having any way to monitor them; or assuming 70g vibration levels at the pump;
or not knowing the exact configuration of a pump that is behaving oddly.  Without good data, it is inevitable
that incorrect conclusions will be drawn, no matter how good the intentions of
the observer.

Chris Zavatson

N91CZ

360std

www.N91CZ.net

“passionate not pationate”

On Tuesday, May 6, 2014 9:21 AM, Wolfgang
<Wolfgang [at] MiCom.net> wrote:

Chris, you are clearly pationate about what you
do but I still say here you're not the only, let alone the final
answer.

 

I think it improper and do not appreciate you
make assumptions on what others have experienced without first hand knowledge
(Lorn) and what I have or not said in the past (You had asked what their
purpose was.)

 

As I have said before, you go to great lengths to
support yourself but give only passing support to the "other side". This is
"fair and balanced" ?

 

Wolfgang

 

-----
Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank" ymailto="mailto:chris_zavatson [at] yahoo.com">Chris
Zavatson

Sent:
Monday, May 05, 2014 7:14 AM

Subject:
Re: [LML] Re: Gear Down...INOP

Wolfgang,

The concept I
have trying to describe here and in my hydraulics write-up is nothing
new.  It is however difficult, if not impossible, to
identify without instrumentation.  Most often this
phenomenon simply causes what is perceived as a hesitation during gear
extension.  Sort of a quick Start-Stop-Start with the gear
continuing all the way down.  It becomes quite clear what
is happening if one looks at the system pressures when gear-down is
selected.  Analog gauges are best for catching the
interaction.  What you�ll see is a pressure pulse just as
the gear starts to fall.  The magnitude of the pulse is
made greater by a few factors: 

1. Warm/hot hydraulic
   fluid (lower viscosity)
2. Outback gear (adds
   gear down force)
3. High-side pressure
   well above nominal (descending into significantly warmer air)
4. Original, lower
   volume gear pump

When the landing gear is in
the retracted position, it stores a lot of potential energy. 
This is from the mass of the landing gear, the pressure on the high
side circuit and, with the outback gear, the aero loads trying to pull the
gear down.

It
is useful to look at Figures 9 and 10 in the hydraulics write-up when trying
understand the chain of events. 

http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf

In Figure 9,
you�ll see state of the pump while the gear is retracted. 
When beginning the extension cycle, the pump builds up pressure
behind the spool (right side) and pushes it against the poppet valve on the
left as seen in Figure 10.  Opening the high side poppet
valve opens a path for fluid from the high side circuit to return back to
the pump.  It is not just the pump moving fluid
though.  All the stored energy in the system is released
and the falling gear, now also pushing fluid back to the pump. 
Given the fixed volume nature of the gear pump, it can only absorb
fluid at a certain rate.  If the gear pushes the fluid
back faster than the pump can absorb it, back pressure builds up in the high
side circuit.  With enough back pressure the spool is
pushed back to the right.   As this happens, the high
side poppet starts to close off again.  Pressure begins to
rise and propagates backwards through the system.  As soon
as the low side pressure rises above the pressure switch set point, the pump
is shuts down. 

Most of the time, the
shut-down is momentary.  This is because the pump takes
time to spool down and it is still moving fluid as it does so. 
At the same time, the falling gear is losing energy. 
If the pressure spike was small, the pump side will win, the spool
will again open the poppet all the way and the gear comes down. 
If the spike was large, the pump will remain off and you will see
equal pressure in the high and low side, just like in Lorn�s
photo.  Pressure will be just above the set-point of the
low side pressure switch and the gear will be partially
extended.  Mitigation simply involves raising the low side
pressure set-point so that the pressure spike can no longer affect the
switch and pump.

I really don�t expect you to
be convinced.  I post these details for the benefit
everyone.

For many years
now, I have been publishing all kinds of reports, studies, diagrams,
maintenance guides and videos of Lancair systems is to promote a better
understanding and safe operation of the LNC2.  If I have
made errors somewhere, please point them out.  But don�t
just say it is wrong or that you don�t agree. Please provide some
legitimate, logical reasoning, some data or something that makes the
point. 

To be honest, I found many of
your posts to be a bit worrisome.  They left me with the
impression you did not have a full understanding of the pump operating
environment or its operation.

For example,
when discussing spool movement, you claimed the pump could be subjected to
70 g�s.  The actual environment is much more
benign.   Vibration peaks are more on the order of
0.1 G�s.  Below is a link to a vibration study that looks
at airframe vibration in different phases of flight.  The
study was done while looking into an engine isolator issue, but is a useful
environmental baseline for anything mounted to the
structure.   

http://www.n91cz.net/Vibration/Vibration_Summary.pdf

Another example was a
question regarding the ball and spring in the return line. 
You had asked what their purpose was.  This would
normally a very legitimate question.  My concern was that
you had already designed a circuit to alter pump operation without being
aware of or understanding the function of all the internal parts.

Innovation is a good thing,
but on an aircraft the level of required due diligence is quite
high.

Lorn�s pump
definitely had issues.  Mounting the pump behind the
baggage bulkhead is not ideal. It discourages good maintenance practices,
just as it did in this case.  Being unwilling to remove it
from the aircraft to investigate the internals because it was �so hard to
get to� simply makes it impossible to properly investigate a
problem.  When I offered to examine the pump, the response
was that these airplanes were built to fly and two weeks of down-time was
too much of a burden.  That was unfortunate. 
Based on Lorn�s description of the pumps behavior I strongly
suspected the root cause of its problems would have been immediately obvious
upon examination.  I have disassembled more pumps that I
can remember.  All were made to operate normally once
configured and adjusted correctly. 

Chris Zavatson

N91CZ

360std

www.N91CZ.net

 

On Monday, April 28, 2014 4:59 AM,
Wolfgang <Wolfgang [at] MiCom.net> wrote:

Chris,

 

I remain unconvinced with your theory. You have
suggested that the pump will somehow shut down immediately after it has
started up due to some pressure pulse. The mechanisim of which you have yet
to clarify, let alone demonstrated.

 

I'm tired of your kibitzing and since you have
proven that you can't let it go, I will and leave you to humor
yourself.

 

Wolfgang

 

-----
Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank" ymailto="mailto:chris_zavatson [at] yahoo.com">Chris
Zavatson

To:
lml [at] lancaironline.net

Sent:
Saturday, April 26, 2014 1:28 PM

Subject:
Gear Down...INOP

Wolfgang,

<<�I
believe in redundancy and it looks like you
don't�.�>>

I
am a big proponent of redundancy.  That is redundancy
defined as a true back-up to an otherwise trouble-free
system.

First, I have redundant switches to power the pump
solenoids.  This allows me to raise and lower the gear
in case of the failure of either of the pressure switches. 
It doesn�t happen very often, but it does happen - twice in 17
years of flying my 360. 

I
also have redundant gear down indications.  Two
completely separate systems, separate switches, separate wires and
separate indicators.  The second set of switches is
mounted directly on the over-center links.

I
even carry two iPads and a iPhone - just in case

<<�The
pressure pulse you're talking about will subside (glad you agree) and as
it does, because the cylinder is only partially extended, the
cylinder will continues to extend, the low switch will close again, and
enable the pump to continue . .�>>

The
part you seem to be missing here is that the momentary pulse is not
directly turning off the pump.  Thus when the pulse
subsides, the pump doesn�t just spring back to life. 
The pulse pushes the spool in the wrong direction -against the pump
flow.  This locks the poppet that the pump just opened
up a fraction of a second earlier.  When this happens,
the high side begins to pressurize along with the low side. 
As soon as both sides reach the low side pressure setting, the pump
is turned off.  This is why you see both high and low
circuits pressurized to the same value in Lorn�s
photo.

To
prevent this, the low side pressure settings should be raised. 
800 psi has proven sufficient.  The high volume
gear pump will reduce the size of the pulse since the higher volume pump
is able to absorb incoming fluid at a higher rate.

I
highly recommend pressure gauges for both high and low circuit be
installed in a location visible to the pilot.  The state
of the system can always be verified.  One can
immediately diagnose any in-flight problem.  Leaks can
be caught early.  And adjusting pressure settings is no
longer guess work.

Chris
Zavatson

N91CZ

360std

www.N91CZ.net