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From:  N295VV@aol.com   (n295 v v @aol.com)

Probably the most important aspect of vacuum pump lifetime is what gets sucked
into the rotating vanes.  For this reason, pleated filters should be placed
upstream at any point where the air is being scavaged by the pump.  The
weakest point of this filtration attempt is probably the cheap wrist-band foam
filter that is used on the vacuum adjustment guage.  

There are some great space-age self-lubricating ceramic materials that could
be used in place of the carbon vanes, and I would hope someday that we might
see the advent of a pump that would last 10,000 hours.  The darn things never
fail in VFR--it is always marginal conditions or full IFR.  

David Jones