Vacuum chamber ideas

I am going to build a chamber type vacuum sealer.
Unlike the Food-saver Seal-a-Meal machines that pull a weak vacuum, do
not seal really well and use expensive special bags, a chamber style has an impulse sealer inside the chamber and the product is bagged, set inside the chamber, and sealed after you have drawn a vacuum.
The reason I am going to build this is that prices for the commercial models start around $1,500 and you have to repack a whole lot of food to recoup that kind of money.
I think I have most of the design figured out, but I am unsure how to fabricate the chamber itself. My first thought was to use a stainless steel steam table pan, but I am worried that this might crush in under vacuum, as the thickest one made is only 20 gauge.
My first thought was to make a tubular frame and epoxy some supports that could then be wired to the frame to give some support to the pan to prevent it from crushing.
My next thought was to layer a 1/4 inch of fiberglass on the outside of the steam table pan using epoxy resin.
Then I wondered if the pan was necessary at all or if I could just mold a fiberglass chamber over a chunk of foam or plywood and end up with a chamber that would hold up to the pressure and the cycling.
So I figured that before I went to a bunch of work and watched a failure because it was not quite strong enough, or wasted a whole lot of money overbuilding, I figured I would run it by you guys for your thoughts.
Roger Shoaf
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RS at work wrote:

How about decapping an air tank or gas cylinder and welding flanges to rejoin the end?
Experiment with a paint pot first?
Couple paint pots mouth - to - mouth via a foot flange containing a central shelf?
--Winston
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I have one of the regular ones, cost about $200 new, and it works like a charm. Are you talking about something a lot bigger?
Steve
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Steve B wrote:

Look at a package of bacon you get from the market. No air bubbles, no leaks, no freezer burn.
I had one of the food savers and I did't like paying the price for the bags and I tossed a lot of meat that got freezer burned when the bags developed a slow leak.
Also if the stuff you are sealing is juicy it sucks the juice out of the bag and fouls the pump.
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On Wed, 13 Oct 2010 16:26:23 -0700 (PDT), RS at work

The instructions say to freeze or partially freeze juicy foods before sealing. Over night does it.
--- ---
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Winston_Smith wrote:

What it does is lower the boiling point and it "boils over".
Can you say " Freeze dried ". :-) ...lew...
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You probably have an external vacuum sealer. Seal a meal. The chambers are over a grand. I have thought of making one also. As too cheap to spring for a chamber one. Bags are a lot cheaper and you can package tuna in retort bags for a better product. I was thinking a small stainless sink, but I like the steam table pan idea better. I was going to weld some studs on the bottom to attached some stringers or weld some stringers to the bottom of the sink. Pan sounds better. Then maybe weld a stainless steel bar top grid for sealing. Have not figured out the lid yet, as I would like a transparent lid. I have read about someone using a refrigerator compressor as the vacuum pump. Pulls 28" of mercury, which is what the better chamber sealers claim.
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Califbill wrote:

As my thoughts have evovled over the past week or so, I am thinking about using tempered glass for the top and bottom of the chamber and to use Lexan for the side walls. While lexan is very flexable, my idea now is to glue on ribs to the sides so as the vacuum wanted to suck the sidewalls in, the top and bottom of the ribs would be supported by the edge of the glass top and bottom. Tempered glass is really tough stuff. As an example think about a pinball machine. I have seen this 1/4" glass survive people standing on the glass and slamming down beer bottles etc. In 3/8 or 1/2 you could probably park a semi on top. Shopping around I found a place that would sell me 14 X 16 X 1/2 tempered glass for about $25
If a full vacuum was pulled on a 14" X 16" panel each square inch would have about 15 lbs of pressure pushing on it so the total force against the top would be about 3,360 lbs. and the same for the bottom for a total of 6,720 on the sidewall, If the sidewall was made of 1/4 inch lexan that would be something like 15 square inchis of lexan supporting the 6,720 lbs. so that would be a load of 450 lbs. per square inch so that would definatly support the weight.
For the long side of the side wall, assuming I make this 6 inches high each long side would have to hold back a force of 1440 lbs. While that much force would usually cause the side to cave in, by bonding the ribs to the side If I divided the side wall into 5 segments, that would give each segment only 288 lbs to support. Piece of cake.
Roger Shoaf
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Winston wrote:

I am going to need a chamber that is somewhere in the order of 14X14X6 inches. If I went with a chunk of pipe, that would have to be something like 16" diameter. The down side to this would be cost and bulk. The more empty space inside the chanber the longer evacuation time.
Also if I used a 16" inch pipe it would also be difficult to make a door. The door would have to be hinged and by the time I dod all of that work, it would get pretty pricy.
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RS at work wrote:

Sounds like a use for an oilless compressor tank after the pump fails. See curb. :)
http://www.northerntool.com/shop/tools/product_200427568_200427568 http://cgi.ebay.com/PALLET-NON-WORKING-AIR-COMPRESSORS-/380278175787?pt=LH_DefaultDomain_0&hash=item588a58782b
--Winston
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In article

Trivial to make a door. No hinge required. Take a 6 inch length of 16 inch pipe, weld a plate on the bottom (years of vacuum experience says 1/4" steel plate would probably do nicely, thinner would work if you domed it a tad) and put a flange (better yet, get 6" with a flange cut off a pipe at the junkyard) with an o-ring groove (hey - metalworking!) on top. A crapped out 16" valve body and a blank flange for the bottom might doing it from stock parts with no cutting. For 16" a 1" Lexan top (if you want to see what happens) should work - we used 1-1/2 or 2" for a 24-30" dia unit much like this (a bit bigger) that was primarily used for vacuum-casting epoxy. The vacuum holds the lid on quite well indeed. Making it cheaply is a matter of picking the right junkyard (try one that gets stainless steel scrap from a university), and seeing the right things in the junk.
If you want the opposite of doing it right, try a 12" port and a sheet of window glass. Does a heck of a job on a tubomolecular pump running full speed (it didn't break right away, so the researcher/culprit actually got the high vac pump running before he filled it with glass shards.)
If evacuation time is an issue for you at food-sealing pressures, you need a better pump...
--
Cats, coffee, chocolate...vices to live by

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Dumb question guys - why not place the bagged food inside a pressureised chamber with the mouth of the bag exiting from a gap/slit in the pressure chamber?
Applying air pressure inside the chamber would force excess air etc from the bag which could then be sealed.
/--------------------\ / \ ========##BAGofFOOD## ====< air press in. \ / \--------------------/
^ ^ ^ heat seal here
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Dennis wrote:

Think toothpaste. :)
Otherwise I like your idea.
--Winston
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Dennis wrote:

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
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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
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Lloyd E. Sponenburgh wrote:

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 didnt 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
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In article

There is the pressure of any air space in the bag/contents. ie, the bubbles you mention below...

Well, in practice, you have to deal with all the splattered "ketchup" on the part of the bag you are trying to seal. Yes, I realize that you are not actually sealing ketchup. But air leaving the food will tend to bubble or even foam (depending on the food) and those bubbles will break and splatter any liquid onto the interior of the bag (...and possibly the exterior, and the chamber, and into the pump if you didn't deign to avoid that).
The chamber I described before which was used for degassing epoxy had epoxy splattered over most of the interior, and a good operator needed to be ready to valve off the pump in a hurry on the initial pumpdown, to let the bubbles sort themselves out without wasting a lot of epoxy foaming its way out of the container. Then you'd sit at max vacuum for a while waiting for the bubbles at the bottom (under the pressure of the epoxy above them) to grow large enough that they would come to the surface and pop. A really fancy system would have poured the epoxy under vacuum (which would get more bubbles out), but that was too much money on fancy things that would move inside the chamber, at least for our budget.
--
Cats, coffee, chocolate...vices to live by

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In either scenario.

You're not using a bell jar, you're using a plastic bag. OF COURSE there is direct pressure (of 14.7psi) on every square inch of food in contact with the bag. Where do you suspect that force would come from in your "pressure packed" example, except from a differential between the inside and outside pressures?

F'criminy's sake... it's not a bell jar. It's a soft plastic bag! It conforms to the surface shape of whatever is in it. It applies PRESSURE to that surface, just as if someone had stepped on it. .... snipped a bunch of non-sequitor stuff...

I'll let you continue to believe that until you see how a continuous fill/seal line actually works.
In the case of potato chips and nitrogen fill, it has nothing to do with differential pressures. The "chamber", when it exists at all, is a room, with no pressure hardware, and no need for it.
LLoyd
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On Oct 18, 8:40am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

Not if the whole bag is inside the vacuum chamber.
jsw
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True enough, but that's not the example he offered. LLoyd
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