"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