Why you should always use a good vacuum chamber...

[CarefulGrower]

Good example of why you should use a desiccator, or really strong stainless steel pressure vessel to vacuum purge bho, quite the reaction -

http://www.youtube.com/watch?v=7AH47oZKhpI

 

[Gray Wolf]

Good point! If you put 14.7 psi over enough area, you can develop tons of force.

 

[Mr Celsius]

Implosions are funny. Acrylic has a nice effect on ethanol in that the acrylic splinters and while under purge it imploded on me.

 

[CannabisTHC]

Great timing right as I'm looking for a dessicator on ebay, makes me think twice about which dessicator to buy, I would not appreciate that happening to me.

 

[Kushed_]

Not a very structural shape to pull a vacuum in, not to mention the huge window!

 

[vertigo0007]

Great timing right as I'm looking for a dessicator on ebay, makes me think twice about which dessicator to buy, I would not appreciate that happening to me.

Pvac and vac it pro on ebay have the best seals thst ive found on a stainless pot style chamber.

 

[CannabisTHC]

Pvac and vac it pro on ebay have the best seals thst ive found on a stainless pot style chamber.

Thanks a lot ! I was hoping someone would comment on ebay dessicators.

 

[CarefulGrower]

Try to get one that has 2 valves on the top, if it doesn't they can add one for $2. Prevents lots of headache.

 

[OGShush]

Anyone implode a mason jar yet? The first thing we did with our vacuum pump was try to implode one at room temperature. Even a quart jar took a full vacuum without imploding, I was pretty disappointed but far too chicken-shit to see if rapidly heating the outside would make it happen.

I can second the vac it pro from ebay, probably the best chamber you are going to get for the price. The guy can be a little slow to ship though, so order it a week before you need

 

[Gray Wolf]

I've never imploded one up to a quart size, but know folks who imploded a quart. I suspect it depends heavily on the integrity of the jar.

Glass' modulus of elasticity is the same as that of aluminum, or 10,000,000, as compared to that of steel, which is 30,000,000, so the same amount of force will deflect it three times as far and glass does not like bending moments that places the upper surface of the bend under tension.

In the case of vacuum, everything is under compression, which is why the jar will take 14.7 psi atmospheric pressure, but would explode under 14.7 psi internal pressure.

One thing to consider, is that glass is a crystaline structure, and that small crack started at any of its grain boundaries, can propogate instantly if flexed, and when you release the vacuum it can explode.

In a former lifetime, I tested windows that I designed in a test buck, where we subjected the windows to the equivalent air pressure that they would see at different elevations. For residential windows at the time, we had to subject them to the equivalent of a 90 mile per hour wind.

It was scarry to watch, because both glass and aluminum are so flexible, that the windows bow in a tremendous distance without failing and the actual mode of failure, when watched in slow motion, is that the window panel bows so far and becomes so short as a result of the bowing, that it jumps out of the window channel and suddenly straightens out.

It is the suddenly straightening out that causes the windows to explode, not the initial flexure.

 

[OGShush]

It was scarry to watch, because both glass and aluminum are so flexible, that the windows bow in a tremendous distance without failing and the actual mode of failure, when watched in slow motion, is that the window panel bows so far and becomes so short as a result of the bowing, that it jumps out of the window channel and suddenly straightens out.

It is the suddenly straightening out that causes the windows to explode, not the initial flexure.

Thanks for the quick science lesson Gray Wolf, your posts are always so informative. I've seen the flex you speak of first hand, in my past life I had a much less interesting job putting in windows like that. I remember my boss coming unglued when he walked around the corner to see two guys carrying a big plate glass window horizontally instead of vertically.

 

[Waxmasta Flex]

WTF was that thing?

 

[grow nerd]

http://www.gnbvalves.com/pdf/EngineeringaBetterVacuumChambe.pdf

 

[Kushed_]

http://www.gnbvalves.com/pdf/EngineeringaBetterVacuumChambe.pdf

Interesting chart. I thought the cylinder with flat ends would have rated higher. This is the shape of alot of ebay vac chambers. It was only two higher than a box! Replace the flat with domed ends, and you go to #7. A sphere is #9

 

[Gray Wolf]

A cylinder of metal will withstand high pressure and high vacuum, because metal is strong in both tension and compression.

The ends are weak simply because they deflect with the pressure, where the wrapper (sides) cannot.

To prevent them from deflecting requires making them thicker in the direction that they are bending. You can also add ribs that increase their equivalent thickness, which is what I did for large vacuum chamber surfaces in industry.

Here is a picture of a dual vacuum interlocked inert atmosphere welding chambers that I designed for welding titanium aircraft parts in an argon atmosphere, after entering the inert atmosphere chamber through a vacuum interlock to exclude atmosphere and remove residual moisture.

Note the end door size and ribs as well as the sides of the vacuum interlocks where you can see them. The ribs make the thinner panels act like a panel of the same overall thickness.

 

[JColtrane]

Very impressive GW!

 

[knucklehead bob]

Not a very structural shape to pull a vacuum in, not to mention the huge window!

Agreed , proves the line , "common sense is uncommon" .

 

[gunnaknow]

Nice craftsmanship, GW. Did the workers wear pressurized suits, or did they wait for the argon to fill the chamber before entering?

 

[Kushed_]

Yes Gray Wolf, very impressive!

 

[Waterpumpee]

Pvac and vac it pro on ebay have the best seals thst ive found on a stainless pot style chamber.

Vac-it Pro certainly is a great rig at a very affordable price-point.