Don Hammer wrote:
Originally, at least, the vacuum came from a venturi in the
slipstream. It was a natural to use a vacuum pump with the same
instruments.

Right. I've seen a venturi on an old aircraft. You can still buy
them. They cost about as much as beer money, and are pretty reliable
unless a bird hits them or they ice up. I understand from the
designer's point of view the drag they create hurts performance much
more than an engine driven pump...

Thanks to all who provided examples of current aircraft that use
pressure pumps. Looking more closeley in my Aircraft Spruce catalog,
it has a couple pumps with separate part numbers- for "vacuum system"
and "pressure system." Most everything else is simply described as
vacuum.

Also, thanks to the two or three guys who gave short physics lessons
without being condescending, although I already understood that "push
here" = "pull over there"

Lots of good help on this group. Keep the fender washer jokes coming.