= -----Original Message-----
From: Chris Zavatson <chris_zavatson@yahoo.com>
To: lml <lml@lancaironline.net>
Sent: Fri, Mar 2, 2012 5:56 am
Subject: [LML] Re: 320/360 Hydraulic Pressure Switch

Wolfgang,

<= /SPAN>

It is a= sad day when removing a pump from the aircraft is too much effort to inves= tigate an anomaly.

Wolfgang wrote:<<We= would all like to get at the root cause of the problem but, as yet, that h= asn't happened. Likely because it's too much work to track down the actual = cause and fix it. =E2=80=A6>>

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As airc= raft owners we are responsible for knowing the configuration of the aircraf= t systems. If something is out of the ordinary, investigate.&nbs= p; We know a lot about what the configuration should be and how it works an= d behaves. We also know of c= onfigurations that do not work. You may very well be holding the key to a new, as of yet, uni= dentified failure mode, but we may never know.

<= /SPAN>

Wolfgang wrote: <<= ;So far we only have a good plausible theory missing only demonstratable pr= oof.>>

If my tire has a flat and I see a nail sticking thro= ugh the side wall, I am rather confident in assuming the nail was the sourc= e of my leak. Likewise, if I= open up a lock-up prone pump and find return springs, I will have a high d= egree 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.

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Wolfgang wrote:<<=E2=80=A6original s= uspicion of the spool coming off it's end point (with the help of springs a= nd airframe vibration) is in fact what's causing the problem.>>

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Springs definitely - that is what they were designed to do. Oildyne started adding springs to cen= ter the spool to the Legacy pump in ~2003. Our system will eventually fail if these springs are install= ed. Fortunately the vast majority of our pumps do not have them. = If you have springs installed, simply remove them.

<= /SPAN>

Vibrati= on - the evidence says otherwise. Measurements of various spool and p= ump 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 vibra= tion 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.

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Wolfgang wrote:<<If it takes that mu= ch force to move the spindle against the O-rings then those springs must be= pretty darn strong. I find that dificult to accept.>>
The spr= ings 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.
&= nbsp;

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?

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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 inst= alled 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.&= nbsp; I have already discussed the benefits of momentary switches not relat= ed to hydraulic lock-up.

Wolfgang wrote:&= lt;<In the event of a problem you have to make sure you push the right s= witch.>>

One sho= uld label the push buttons appropriately.

<= /SPAN>

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 Oil= dyne spec sheet ?>>

Recall = that the Legacy pump configuration =E2=80=9CCZZ=E2=80=9D is proprietary to = Lancair. Companies generally= don=E2=80=99t post proprietary materials on-line.

<= /SPAN>

<<You seem to want to be "involved"= in the anomalies of flight.>>

Not really. I avoid th= em by thorough examination, no matter what it requires.

Chris Zavatson

N91CZ

360std

www.N91CZ.net

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