First the AI, then the DG, then...?

"Jay Honeck" wrote in message news:fXJxb.334160$HS4.2853565@attbi_s01...
A friend of mine says that the gyros inside ride on some sort of a "ruby
bearing" -- and that they eventually wear out. Sometimes the rotor (or
whatever) even falls right off the bearing. When that happens, everything
just stops -- like mine did.

Or something like that. Either way, it's just more money...

Little wee tiny ball bearings. The lube dries out from all
the air going through the instrument, cold weather hardens it,
airborne pollutants get through old/cracked/nonexistent filters
(cigarette smoke is a bad one) and bearings can't take it anymore.

Dan

Jay Honeck wrote:
: Short of replacing the vacuum pump itself (which is still working fine), is
: there anything else I should be watching?

As others have said, check the accuracy of the vac gauge, because extra-high
vacuum will make the gyros "over-rev" and wear their bearings quite quickly.

You might want to look at the inline filter STC that inserts a filter in the
suction line between the regulator and the vacuum pump. The theory is that
if the pump fails, the carbon vanes blow up into dust which gets sucked back
into the lines and instruments by residual vacuum. This in-line filter
supposedly traps all of that carbon dust, preventing the lines, regulator,
and instruments from becoming contaminated. When the pump is replaced, the
filter needs to be replaced as well.

As I recall, the same fellow that holds the M-20 air/oil seperator STC holds
this in-line vacuum filter STC.

--
Aaron Coolidge (N9376J)

"Jay Honeck" writes:

As a precaution
(I'm assuming some sort of contamination caused the second failure), I've
ordered new vacuum hoses -- enough for my A&P to replace all the hoses, from
the vacuum pump to the firewall, and from the firewall to the two vacuum
instruments. I'm also having him replace all the filters.

A somewhat dumb question. Each vacuum-driven instrument has its
own input filter, correct? The hoses and pumps are then all downsteam
of the instrument.

Does garbage really migrate upstream into the expensive toys? (And
if so, you'd thunk someone would add a inline filter between the
toy and the common vacuum line..)

Education welcomed.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

David Lesher wrote:

Does garbage really migrate upstream into the expensive toys?

If a dry pump fails, the carbon vanes may turn into powder. When this happens,
the pressure on the instrument side is lower than atmospheric pressure, and you
may wind up with some of this powder being blown back into the instruments. In
normal use, however, garbage does not migrate back upstream.

(And if so, you'd thunk someone would add a inline filter between the
toy and the common vacuum line..)

Some people do this as a preventative measure. Alternatives include prophylactic
replacement of the dry pump to attempt to ensure it never fails, using a wet
pump, and cleaning the instruments before using them after a pump fails. The
filter is cheap insurance.

George Patterson
Some people think they hear a call to the priesthood when what they really
hear is a tiny voice whispering "It's indoor work with no heavy lifting".

"G.R. Patterson III" wrote in message ...
David Lesher wrote:

Does garbage really migrate upstream into the expensive toys?

If a dry pump fails, the carbon vanes may turn into powder. When this happens,
the pressure on the instrument side is lower than atmospheric pressure, and you
may wind up with some of this powder being blown back into the instruments. In
normal use, however, garbage does not migrate back upstream.

(And if so, you'd thunk someone would add a inline filter between the
toy and the common vacuum line..)

Some people do this as a preventative measure. Alternatives include prophylactic
replacement of the dry pump to attempt to ensure it never fails, using a wet
pump, and cleaning the instruments before using them after a pump fails. The
filter is cheap insurance.

George Patterson

A failed vac pump isn't likely to send garbage back up the line.
The instruments represent a significant vacuum leak, and the pressure
will drop off almost instantaneously when the pump fails. The filters
between the gyros and pump are more likely to keep garbage from a
failed instrument from gettingn into the pump, failing it as well.

Dan

David Lesher
shared these priceless pearls of wisdom:

-
-A somewhat dumb question. Each vacuum-driven instrument has its
-own input filter, correct? The hoses and pumps are then all downsteam
-of the instrument.

Sometimes. More often there is one very large filter with two outlets (or a
single outlet with an installer's T fitting) for both vacuum gyros.


-
-Does garbage really migrate upstream into the expensive toys? (And
-if so, you'd thunk someone would add a inline filter between the
-toy and the common vacuum line..)

Not really. The carbon dust that comes off of a normally operating pump gets
ported overboard and the big chunks that come off of a pump in failure mode get
thrashed about until they are small enough to be blown overboard OR remain in
the pump as mute testimony to the advantages of a wet pump.


-
-Education welcomed.

And is generally expensive, but not as expensive as ignorance (Twain).


Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
600,000,000 times in 1000hrs.

Mike
MU-2

"Jay Honeck" wrote in message
news:1lzxb.331132$Tr4.1006704@attbi_s03...
A couple of months ago our AI, which had been "coming and going", finally
went. We replaced it with a rebuilt unit from "The Gyro House", which had
the dual effect of getting our autopilot working properly again.

Last month, our DG failed completely and suddenly, after a normal landing
in
Pella, IA. Before that landing it worked, after that landing it didn't.
And the autopilot -- connected to the DG, too -- stopped working again.

So, I've just received a rebuilt unit from the Gyro House. As a
precaution
(I'm assuming some sort of contamination caused the second failure), I've
ordered new vacuum hoses -- enough for my A&P to replace all the hoses,
from
the vacuum pump to the firewall, and from the firewall to the two vacuum
instruments. I'm also having him replace all the filters.

Short of replacing the vacuum pump itself (which is still working fine),
is
there anything else I should be watching?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Mike Rapoport" wrote in message
link.net...
How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
600,000,000 times in 1000hrs.


I hate to think how many revolutions my 7200RPM hard drive makes in a year
(24/7).

But you HDD was sealed in a cleanroom. Vacuum gyros are constantly
injesting grit.

Mike
MU-2


"Tom S." wrote in message
...

"Mike Rapoport" wrote in message
link.net...
How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
600,000,000 times in 1000hrs.


I hate to think how many revolutions my 7200RPM hard drive makes in a year
(24/7).

"Mike Rapoport" wrote in message hlink.net...
How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
600,000,000 times in 1000hrs.

Mike
MU-2

I think it's a lot higher than that, maybe as much as two or three
or four times. Plenty, anyway.

Dan