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