Vacuum chamber ideas

Sounds like the same technique that is used in hot wire anemometers. One common application of that would be the MAF sensor in many cars. I don't know if there are any generic controllers that would suit your purpose.

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=92t 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

The problem with using a thermocouple is getting the thremocouple to react faster than the plastic. A thick freezer bag is only ,004" thick and it is really easy to over shoot the temp. if you try to use a thermocouple.

The budget way is to use just time and trial and error. This works if your timer is consistant and the residual heat is allowed to blead off. Otherwise it is like making toast, the first slice tends to be a little lighter than the ones that follow as the toaster is already hot.

On the other hand, your controller might work if you can use a coil to measure the amp draw of the heating element, and use that instead of a voltage of a thermocouple. You might need an additional circuit to translate the signal so the controler can understand it. When I get to the control phase of the project I might run this by a electronics whiz friend of mine.

My suspicion is that you can probably get a good seal using a timed pulse and trial and error.

Roger Shoaf

Not if the whole bag is inside the vacuum chamber.

jsw

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.

RS at work fired this volley in news:94d50a8b- snipped-for-privacy@g20g2000prg.googlegroups.com:

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

Jim Wilkins fired this volley in news:2ce79227-8037- snipped-for-privacy@h7g2000yqn.googlegroups.com:

True enough, but that's not the example he offered. LLoyd

The original proposal:

"I am going to need a chamber that is somewhere in the order of

jsw

Jim Wilkins fired this volley in news:b0602d4d-bd61- snipped-for-privacy@a36g2000yqc.googlegroups.com:

If that's what he originally posted, and IF he intended to do all the sealing operations within the vacuum in that chamber, then I agree with what he said.

Not a jot or tiddle of this post showed up on my news reader, and it's usually reliable in that respect.

LLoyd

Of course I'm familiar with the expression "jot or tittle", but having never encountered "tiddle" before except in the Monty Python song where it's meaning doesn't matter, had to look it up. From the 1913 Webster's Revised Unabridged Dictionary, tiddle is a verb that means "To use with tenderness; to fondle" -- which most news readers aren't noted for.

James Waldby fired this volley in news:i9iu1e$7bs$1 @news.eternal-september.org:

It's a noun, too:

"A tittle, rather appropriately for a word which sounds like a combination of tiny and little, is smaller still (than a jot). It refers to a small stroke or point in writing or printing. In classical Latin this applied to any accent over a letter, but is now most commonly used as the name for the dot over the letter 'i'. It is also the name of the dots on dice."

LLoyd

"Lloyd E. Sponenburgh" fired this volley in news:Xns9E15E6A8C9895lloydspmindspringcom@216.168.3.70:

oops... a cite

And the more surface area, the greater the force applied by the atmosphere. Given your 14x14" dimension, that is 196 square inches, and given an average atmospheric pressure of 14.7 psi that is 2,881 pounds force which the walls will have to survive.

The 16" pipe would have 201.6 square inches, or 2,955 lbs on the end plates.

I have my doubts about glued up acrylic (Plexiglas) handling that.

Good Luck, DoN.

I dunno. This 24" x 24" x 24" cube looks really neat, though!

--Winston

Yes, it does. But ...

2) It is sealed by an O-ring to a flat machined metal surface.

4) The enclosure is *not* Plexiglas. I don't know the metal involved. Perhaps stainless steel, perhaps aluminum. If the latter I would expect metal fatigue over the years as the number of pressure/vacuum cycles builds up.

I kept reading (earlier in the thread) plans for gluing up a box of Plexiglas -- and *that* I do not trust -- especially in normal thicknesses.

Enjoy, DoN.

See comment at end re "glued up" version

...

Per the door is acrylic rather than polycarbonate. Metal can be aluminum or stainless steel as buyer prefers.

The interior dimensions of the VCC-24 cube in the image are

Roger's description wasn't clear -- his mention of bracing ribs was vague -- but here's my interpretation: He said the top and bottom would be square plates of 1/2" tempered glass. These are the faces that would take the 2881 pounds of pressure you mentioned in earlier post. No glue involved in bearing that load. The sides would be thicker Lexan (polycarbonate), "braced by ribs". Presumably two sides would be braced at their ends against the other two sides, which are somehow braced apart by "ribs".

I think it would be a better design to rabbet the ends of the sides so that bracing is symmetric, and to center say

DoN,

I appreciate your criticism.

I find that the process of designing something even more satisfying than building the thing it self. I have set an arbitrary goal of $200 for building this project, which may or may not be doable; nothing is cast in stone yet.

For the top of the chamber I was originally thinking about some 1=94 Lexan, then I priced the stuff, not cheap.

I then asked myself how strong does it have to be? And, is there something else that can do the job cheaper?

Tempered glass is pretty strong stuff. I have seen a 200# person stand on the glass of a pinball machine. And that is only 1/4=94 thick. In checking a bit, I noted that one glass company shows a guy jumping up and down on a sheet of 3/8 supported on wood blocks about 5 feet apart. I also noted that people build big aquariums out of glass and acrylic glued together and supporting holding tons of water.

While I am not sure, I suspect that a clear span of 14=94 X 16=94 X 3/8 or

Assuming I will get a satisfactory reply to the glass inquiry, the plastic sidewall I described admittedly sounds like a failure waiting to happen, but here is my thinking.

Assume that you have a nice thick chunk of 6=94 pipe sealed on one end, and on the open end you have a sheet of Plexiglas and a rubber gasket. If a vacuum were drawn out of the pipe would a 1/4 sheet of acrylic have the ability to resist fracture if you got near a full vacuum? I think it would, as it is about 300 lbs. evenly applied over about 19 square inches.

Now if you can accept that proposition, think about a 1/4=94 sheet of Plexiglas that is 6 =93 by 4=94 and has a 1/4=94 X 1/2 bonded to each one o= f the 4=94 ends and between and along the 6 inch sides you have two 3/8 thick sides that are 1 inch high and are tee shaped with the top of the tee being 1/2=94 high 6 1/2=94 wide and the bottom being 5 1/2=94 wide and bonded to the ends with the tabs sticking out.

What you would have would be a Plexiglas box with 1/2=94 sidewalls and 4 tabs that are 3/8=94 X 1/2=94 X 1/2=94.

If you were then to suspend this box on the tabs between two rails and loaded the box with 360 lbs., would it hold? I think it would.

Now if I haven=92t lost you yet, the top and bottom of the chamber are going to be exerting a total force against the sidewalls of about

As far as the glue joints go, the glue joints should be stronger than the plastic itself.

If my thinking is off here I would like to know where. The regular RCMer=92s tend to be a bunch that is pretty damn smart, which is why I tossed the concept out there.

The cost between Plexiglas and Lexan is not much, so I might opt to go that route, also I might increase the number of side support ribs to spread out the load a bit more to increase the safety factor, it kind of depends on the yield I can get from a stock sheet of plastic.

Thanks again for your criticism.

Roger Shoaf

The door glass on these is 5/8" thick:

jsw

OK lets see if I can make it clearer.

____________________________________ ______ | | | Tempered glass | | | ____________________________________| | | | |_C1__| | | | | | | | | B | | | | | D | | A| | | | | | | ~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~ | | | | | | | | | | | | | | ______| | ____________________________|__|__C2__| | | | Tempered Glass | | ____________________________________| | | | | | |______________|

Hopefully this will work.

(A) is the sidewall. (B) is a vertical rib. (C) are horizontal stiffiners. (D) is an ell shaped piece, but might be fabricated together with part (B).

Where the bottom glass meets part A and C2, this will be sealed with silicone sealant.

Where the top glass meets part A and C1, there will be some sort of rubber gasket.

Parts A, B, C1, and C2 will be bonded.

Part D may be bonded to parts B, C1 and C2 or could be fastened to part B with screws if I want to make it so I can take it apart, but then might have to be made from thicker material.

Roger Shoaf