Wolfgang,
It
is a sad day when removing a pump from the aircraft is too much effort to
investigate an anomaly.
Wolfgang
wrote:<<We would all like to get at the root cause of the problem but,
as yet, that hasn't happened. Likely because it's too much work to track down
the actual cause and fix it. …>>
As
aircraft owners we are responsible for knowing the configuration of the
aircraft systems. If something is out of the ordinary,
investigate. We know a lot about what the configuration should be and
how it works and behaves. We also
know of configurations that do not work.
You may very well be holding the key to a new, as of yet,
unidentified failure mode, but we may never know.
Wolfgang
wrote: <<So far we
only have a good plausible theory missing only demonstratable
proof.>>
If my tire has a
flat and I see a nail sticking through the side wall, I am rather confident in
assuming the nail was the source of my leak. Likewise, if I open up a lock-up prone
pump and find return springs, I will have a high degree of confidence I have
found the source of the problem.
Could there be a second cause?
Possibly, but as of yet, none have been
documented.
Wolfgang
wrote:<<…original suspicion of the spool coming off it's end point (with
the help of springs and airframe vibration) is in fact what's causing the
problem.>>
Springs
definitely - that is what they were designed to do. Oildyne started adding springs to
center the spool to the Legacy pump in ~2003. Our system will eventually fail if
these springs are installed. Fortunately the vast majority of our
pumps do not have them. If you have springs installed, simply
remove them.
Vibration
- the evidence says otherwise. Measurements of various spool and pump
combinations required from 13 g's (9 year old 'soft' o-ring) to 70
g's (new 'stiff' o-ring) to move the spool. Aircraft vibration at
the pump was measured to be +/- 0.1 g (flying) to +/-1.3 g (engine start).
Vibration is not nearly sufficient to have any effect on the
spool.
Wolfgang
wrote:<<If it takes that much force to move the spindle against the
O-rings then those springs must be pretty darn strong. I find that dificult to
accept.>>
The
springs are very strong, 26 lb/in.
Wolfgang
wrote:<<Vibration
levels can exceed 70 G's>>
See
MIL-STD-810 for expected vibration levels in aircraft
environments.
Wolfgang
wrote:<<Yes, that would be easy . . . except . . . you can only override
one pressure switch at a time or overload the
system>>
I
would still like to know how push buttons can overload
anything. And why would anyone want to override more than one at a
time?
Wolfgang
wrote:<<The items you cited are more a one-of condition
...>
I
have never had a thermal lock up, yet I use pressure gauges and the momentary
push buttons on a regular basis. They were originally installed to deal
with sticking VEP switches, but it is like getting a new tool. After you
have it, you can't imagine how you lived without out it. I have already
discussed the benefits of momentary switches not related to hydraulic
lock-up.
Wolfgang
wrote:<<In the event of a problem you have to make sure you push the
right switch.>>
One
should label the push buttons appropriately.
Wolfgang
wrote:<<Are you saying that Oildyne is putting springs in the spool to
center it when the pump is not running ?
Springs
that are not documented in the Oildyne spec sheet
?>>
Recall
that the Legacy pump configuration “CZZ” is proprietary to Lancair. Companies generally don’t post
proprietary materials on-line.
<<You
seem to want to be "involved" in the anomalies of
flight.>>
Not
really. I avoid them by thorough
examination, no matter what it requires.
Chris
Zavatson
N91CZ
360std