Lloyd E. Sponenburgh wrote:
RS at work fired this volley in news:45d6e4a8-
:
OK I can answe that. If you were to pressurise the outside of the bag
everything inside the bag would try to escape, including the stuff you
wanted to keep in the bag.
Think about a kid stepping on a packet of ketchup.
Roger Shoaf
Well, Roger, I think, then, that you missed something.
That "kid" is still at work when you pull a vacuum on the bag.
1) the contents will try to escape out the evacuation hole because,
2) the KID weighs 14.7psi at sea level, and he's stomping crap out of
your ketchup.
LLoyd
I don't think you have thought this out. When you start, the air
pressure on the inside of the bad is the same as it is on the outside
of the bag.
The bag is held shut by a less than hermetic seal, so as the air
pressure in the chamber drops, the air pressure inside the bag drops
also, but unlike the kid stepping on the ketchup packet, there is no
pressure on the other stuff in the bag.
Think of what would happen to a cup of ketchup in a bell jar, as the
air pressure drops, any bubbles in the ketchup would come to the
surface and pop but the ketchup would just sit in the cup, assuming of
course that you didn’t hold the vacuum so long as to vaporize all of
the water.
When a deep level of vacuum has been obtained, there might be space in
the bag, but that space contains no oxygen or a practically zero
oxygen level.
When the bag is then sealed, and air pressure is then reintroduced top
the chamber, now pressure is pushing the stuff inside the bag. Unless
the stuff is like potato chips or other crushable stuff, the air
pressure just holds the plastic against the stuff and prevents the
oxygen in the air from oxidizing and the aerobic bacteria from
growing.
Another cool thing you can do with a chamber sealer is to back fill
the chamber with nitrogen or another inert gas. This is what they do
with potato chips to get an oxygen free packaging.
Roger Shoaf