Air is good if your breathing and bad if leaking into your brain.  OK, I'll go out and rebuild one this am and report back.  Oh, but wait, I guess the rebuild of the leaker will have an affect on our test. 

Larry,

 

I love spirited discussions leading to one's spirit sipping spirits during contemplation of the metaphysical.  I thought more about all the problems reported over the years and the possible effect of air.  Let's see if we can work thru this by picking the system apart.  But first, I said you should only introduce air into the system as a test of your theory, not rebuild a cylinder.  

 

 

4 of the six cylinders, those associated with the main gears and doors, can be eliminated because they are oriented horizontally with all ports pointed upward so the air will not remain in those actuators. 

 

The nose gear door cylinder, vertically oriented cannot hold much air in the bottom after extension because the air would have to fit in a donut cylinder volume 5/32 high with the inside 1/2" diameter and the outside 5/8 diameter - a volume of .017 cubic inches.  This space is inside of the extension piston stop that allows fluid to be passed in and out of the cylinder.  Upon retraction, even though the piston does not tightly reach the top, the fluid exit is at the top and air would be expelled.  The .017 ci of air could be trapped at the piston that is pushed in by the hi pressure retraction activity and the bubble could rise to the bottom of the piston.

 

The nose gear cylinder is somewhat vertically oriented and the cylinder cannot hold any air in the bottom beyond the piston at full extension since it is stopped tightly against the forward bulkhead (if properly rigged).  However, retraction is limited by the external stop and the fluid exit is at the aft lower side of the cylinder.  I forgot to check how vertically oriented the cylinder gets on retraction, but let's say the whole remaining space can retain air.  That is a cylinder approximately 3/4" high with a diameter of 9/8" for a volume of about .75 cubic inches.  Of course, at retraction this pocket would not be under pressure since it is the other side of the piston that is under pressure.  So, it is on extension that some of this pocket could be compressed although it would seem that some of the air would come out at each retraction. 

 

 

There also are short pieces of Easton flexible line that feeds into 1/4" hard Al lines. Let's discuss how much volume these lines can hold.  For the Easton line (I could not find a sample), assume it has an interior cross section of 1/4".   That is 20.37 inches of tube per 1 cubic inch of fluid volume.  The 1/4" hard lines have a wall thickness of .035, thus the interior diameter is .18" or 39.3 inches of tube per cubic inch of volume.

 

Door actuators move about .9 ci of fluid in when extended and .7 ci in when retracted.  The nose gear cylinder (I forgot to measure the length, say 4.5" of movement) moves about 4.5 ci of fluid in when extended and 4 ci in when retracted.

 

Since the opening of doors requires fluid passage thru sequence valves, those lines might not be completely cleared because of the hard line length may hold more fluid than is transferred to and from the actuator.  One could consider a small bubble remaining in those lines.  The retraction side moves more fluid thru shorter lines so it is less likely that air is trapped in those lines.  The large actuators move much more fluid and it is hard to believe any air remaining in those lines.

 

 

The dump valve body can't hold air once it has been opened.  Perhaps the teed vertical lines leading to the pressure switches retain air.

 

 

For those that suspect that heated trapped air raises the system pressure quite a bit should note that when the volume is held constant, the pressure increases as the temperature ratio, in Kelvin, increases.  A rise from 50F to 80F is 299K/283K or approximately a 5% increase - Hardly accounting for a rise of several hundred psi.  I await an engineer to evaluate effects of the differing expansion factors for aluminum, Easton lines, cylinders and the fluid itself.

 

On the converse, if the air is compressed (so far this looks like a problem that is possible solely on the down side at the nose gear actuator), I would finally have to agree that more volume of fluid under pressure from the air would have to pass through the system leak to activate the pressure switch than that from incompressible fluid on its own. Maybe.  That these air pockets may work themselves out so that the chirp rate increases is interesting.

 

So I can see where an accumulator could delay pump activation.  No problem as long as other parts of the system are working properly.  It is hard to see where any air bubbles could influence the up side of the system other than those trapped in the sequence valve circuits.

 

----

 

As to some of the other contentions.................

 

You said: "You're an electrics guy.  Does that little chirp every 20 seconds not bother you just a little?  You know, arcing and corrosion in the relays, airborne fire, alternator shorting, etc?"

 

You are correct, the wiring is correct.  Thus, arcing and corrosion are not a problem - intermittent relays are operating intermittently .  Airborne fire and alternator shorting are not a problem from the pump blips for the small percentage of block time that the gear is down, nor is anything else associated with the hydro-electric gear system.  However, "etc." does indeed bother me, although it is not related to this situation.

 

One of the risks you may add is that the accumulator on the high pressure side may lock up the low pressure side if you have a failure like that sometimes described by other Lancairites and not yet fully understood.  This is the case where opening the dump valve does not resolve the peculiarly built system pressure present on both sides and that trips both pressure switches.  There may be an electrical solution - perhaps bring duplicate wires from the pressure switches forward to secret over ride switches operable by the captain.  Forced activation of the pump may free the lockup if it is the case of a stuck shuttle valve.  Of course the captain's hearing has to be good enough to perform an "undo" if the pump is straining as the captain becomes the acting pressure switch.

 

Good Luck,