William R. Watt wrote:

still the vacuum on the suction side of a vacuum pump is not limited by
atmospheric pressure, even when connected to a vacuum bag set up for resin
curing.

Well, actually it *is* limited by atmospheric pressure unless you
have the bag in a pressurized environment. Evacuate the bag to 0
psia/bara/mm hg/pa/torr/microns (whatever absolute units you want
to use) and the pressure differential between the bag interior and
exterior is simply the ambient pressure. In open air, that's
atmospheric pressure.

all it means is the pump is creating a vacuum greater than
atmospheric pressure and could be run at a lower speed. imagine a vacuum
pump strong enough to suck the resin, hull, and all right into the pump.

Imagine is all you *can* do unless you find an alternate motive
force besides the atmospheric pressure. Sans such motive force
(e.g. pressurized chamber), 14.7 psia is all you have to work
with, on a good day (well, you *do* have bag mass and acceleration
due to gravity, but that works for you on the top side, and
against you on the "bottom" side).

can't do that at atmopheric prssure.

Exactly.

Keith Hughes