"David D." > wrote in message
oups.com...
> I have an impeller pump, but it always seems to introduce a bit of
> oxygen into the wine (connections are sealed tight).

You're seeing degassing taking place, caused by the cavitation of the
impeller (assuming no air leaks).

> There doesn't seem to be oxygen pickup, but can a weak vacuum strip
> some of the wine's character?

A little perhaps. Depends on how long and hard you pump on it.

Tom S