Seeking a cheap wide mouthed jar capable of withstanding a vacuum

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  • #26
Baluncore
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1) Am I making some sort of mistake here?
No mistake that I can see. If you can cap the jar without it falling apart then it should safely hold a perfect vacuum, possibly even if it has a crack in the glass.

There can never be more than one atmosphere of negative pressure, so preserving jars are very safe. Positive pressures must be avoided, but the cap and seal are designed to prevent positive pressures. Any other container will need to be carefully assessed.

2) Is that last two percent that much of a difference from essentially perfectly safe to "RUN FOR YOUR LIVES!"
No. The last two percent to a perfect vacuum are insignificant and quite safe. On the other hand, the last two percent with positive pressure will be as deadly as the last 0.1% because that is when the glass will shatter explosively due to the high internal pressure.

Vacuum is inherently safe so long as you are not in it for long, and you do not stand at the end of a shock tube gun barrel. Air pressure on the other hand can be deadly with only a couple of psi, which is your internal pressure, and getting air under your skin can cause an air embolism with symptoms like the "bends". You should be able to suck a vacuum with your mouth down by 10 psi to about 4 psi absolute. You will not be able to blow 2 psi positive without embolism, probably of your salivary ducts initially, maybe followed by a stroke, depending on where the bubbles go.
 
  • #28
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There's a heavy duty plastic mesh-sleeve made for protecting and containing lab glassware. Comes in different diameters. We used it on glass rotary evaporator condensers etc. Also made for a fair grip on round and pear-shaped flasks, which were so slippery when wet....

That Vac dessicator pic reminds me of when some-one put a red-hot crucible into a too-small *ordinary* dessicator to cool. The lid 'hovercrafted' across and clamped shut. Too tight to slide. We needed the data. We'd settle for the crucible. Smashing the glass dessicator was not a favoured option.

I figured a fix: I put a rubber band around the join, put the small dessicator inside our carefully emptied largest vaccuum dessicator then, very slowly, pumped it down. Ta-da ! Lid lifted, rubber band prevented a re-seal, slowly vent to atmospheric, job done.
;-))
 
  • #29
jim hardy
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If you don't need to see through it, ....

seems to me this type of product already handles vacuum...

upload_2018-5-6_21-46-13.png


not really cheap, though. Thrift shop perhaps?

old jim
 

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  • #30
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No, it only handles the vacuum between the double skins. IIRC, there's a foam spacer to stabilize them.

Can you get hold of some flanged or threaded 'heating' pipe about 4 in (100mm) ID ? Blanking plates etc allow connections to be screwed in...

Hmm. How did the classic 'Scientific American' amateur scientist articles handle this ?
 
  • #31
jim hardy
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No, it only handles the vacuum between the double skins.
My thought was that evacuating it places zero differential across the inside chamber skin . So even using a glass lined one doesn't invite implosion.
 
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  • #33
Baluncore
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I have one of these. The wall thickness is between 3/8 and 1/2 inch which makes it possible to drill & tap fro a pipe thread.
What pressure reduction can you achieve with the green button pump built into the lid?
If the pump works, why do you need to drill the plastic container wall?
 
  • #34
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Since it will be nearly a month before the insects I desire are collectible, today I ordered some vacuum gauges similar to but less costly like these. I have two options for use: 1) either fashion a quick connect/ disconnect system like used for air compressors to only occasionally check on jar vacuum while in the freezer, or 2) use a 1/4" female threaded "t" adapter and keep the gauges on permanently while frozen. I actually prefer #2. According to specs, they should work at freezer temperatures, but I was hoping to confirm if anyone has done it successfully? Thanks.
 
  • #36
arydberg
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What pressure reduction can you achieve with the green button pump built into the lid?
If the pump works, why do you need to drill the plastic container wall?
the green button is not a pump. Unless you release the vacuum the jar is impossible to open. The function of the green button is to release the vacum. My idea is to fit a vaccum hose to a barbed fitting with a pipe thread and thread the fitting on to the vaccum jar as i only have the container and do not have the pump but i have another vacuum pump.
 
  • #37
Baluncore
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The function of the green button is to release the vacum.
Is the big green lump in the middle a handle for the lid or the vacuum release?
What is the much smaller green button in one corner?

Is there a vacuum storage container with an integral pump, or only external?
 
  • #38
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Hello everyone,

I wasn't sure whether or not to start a new thread, or continue this one. Please reread my post #4 above to get an idea of what I have been trying to do.

The idea has been to freeze dry soft bodied insects for preservation. This would include caterpillars, spiders, soft beetles and similar. I initially started with basically a homemade vacuum system using heavy walled 8 oz jars fitted with rubber stoppers and the stoppers drilled to accept plumbing valves to allow vacuum to be maintained after the jar is evacuated by single stage pump (post 4). While this system has worked out nicely, I've been needing to go with something larger. My latest experiment was using mason jars. While I can easily seal the jars this way, and they maintain vacuum well, there doesn't seem to be a reliable way to release the vacuum slowly when the time has come to remove the insect (which generally occurs after being under vacuum for two weeks in the freezer).

After careful saving, budget finally allowed me to obtain one of these, which arrived two days ago. To my disappointment however, this device is not holding vacuum. I applied Dow high vacuum grease to all joints and both sides of the rubber ring at the halfway point of the container sections, but after a few hours in the freezer, I am losing vacuum. I will point out that, in the original article, the author says to NOT grease the rubber ring/ gasket. Not sure why. Can anyone shed some light as to why I am losing vacuum? Is there any way to tell where exactly the leaks are occurring?
 
  • #39
BillTre
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The original article is old. Your device is new.
I would see what the manufacturer of the desiccator you bought says about the issue.
They may also have something like a FAQ or help line where you might get some idea about why it isn't working.
If not the seals, it may have something to do with the valve.
If the manufacturers help doesn't help, there might be appropriate to return it for a replacement.
 
  • #40
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I would see what the manufacturer of the desiccator you bought says about the issue.
They may also have something like a FAQ or help line where you might get some idea about why it isn't working.
If not the seals, it may have something to do with the valve.
Here is what the manufacturer says, so I am right in using the grease. I also swapped out valves for a different one, still getting loss. Any way to tell where the leak may be coming from? Can I take the unit from the freezer and tip it in a tub of water?
 
  • #41
BillTre
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I could not find any directly useful information on the manufacturer's site, but I did see a different view of the desiccator.

The valve is on slip fitting with the dome. It should slip on and off. It could be leaking and should be greased up (unless you already did).
If that doesn't work, I would disassemble the valve, grease the contacting surfaces, and reassemble.
Sometimes just taking something apart and putting it back together can fix it (dust falls out or ring sits properly).

If that doesn't work go to the company you bought it from and tell they you are disgruntled and want some decent information on a product you bought from them. But do it in a friendly way.
They might be able to provide a useful contact at the manufacturer.
 
  • #42
BillTre
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The sealing issue is not in their FAQs, which are few.
You could send a message to the manufacturer here, asking about your problem.
I would do this first if you can't figure out the problem yourself (which is always better).
 
  • #43
BillTre
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They have a tech manual here. Its mostly about properties of the materials their various products are made of.
Not useful for advice, but among many other things, it will list the resistances to solvents of different plastics. Figure out what your item is made of, look it up, and know what not to expose it to.
It is also a good way to know what products to look for if you want to use particular chemicals.

According to the items webpage it is made of PP/PC; probably polypropylene and polycarbonate parts. These are plastics that can take temperatures high enough to autoclave them (common lab sterilization method (you can do it in a pressure cooker!)). However, they might warp, making them more difficult to use.
 
  • #44
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Thanks, BillTre, but all may not be lost yet. I just made one discovery which could be causing reading errors. When I placed the desiccator in the freezer after vacuuming, I also placed a simple oil-filled gauge in on top of the removable tray. This internal gauge began to register vacuum drop from about 28 down to 22" Hg over the course of three hours while in the freezer. However, a separate gauge at room temperature coupled to the desiccator valve shows the original 28" Hg. Therefore, the internal gauge might be in error from the cold. Perhaps the oil contracted or even started solidifying thereby affecting the needle. When I bought the gauge, the ambient temp was supposed to be down to -4 F (according to the specs listed at that website). With my freezer bottoming out at around 1 F, it should work but maybe not. I'm going to let the desiccator continue undisturbed in the freezer until tomorrow and see if vacuum changed any on the external gauge before I go any further.
 
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  • #45
Tom.G
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Their tech manual shows the minimum temperature for PP (polypropylene) as -10°C (14°F).
Also check the chemical compatibility table.
But I agree that the oil filled gauge is most likely the problem of the moment.

Edit 1: You might want to check the temperature rating of the guage.

Edit 2: A gauge is oil filled to increase mechanical damping of the needle. Not needed here as the measurand (chamber pressure) is essentially static. Try a gauge based on an Aneroid Barometer:
https://www.britannica.com/science/atmospheric-pressure#ref128230
http://marinegyaan.com/what-is-aneroid-barometer-its-principle-and-correction/

Cheers,
Tom
 
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  • #46
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Thanks for the replies, guys. BillTre and Tom G, you both seem pretty thorough, something I should have been before using the device as intended. However, after roughly 64 hours in the freezer under vacuum, I tested it today using the external gauge and the good news is that there has been very little, if any, change in vacuum (perhaps 0.5" Hg change but not even sure of that). When I was having vacuum retention problems (or just thought I was), one of the first things I did was change out the original flimsy and press-to-fit valve for one of my copper ones I use for my thick walled jars. I had to epoxy a copper tube in place and then coupled the new valve to the tubing with lab vacuum tubing. I was a bit worried about outgassing from the epoxy (JB Weld), but I read it wasn't an issue unless much greater vacuums were used. The plumbing valves can sometimes leak, so I wanted to be sure it was easily replaceable.

This new chamber with valve seems to be holding vacuum better than my thick walled jars with stoppers. I usually have to re-evacuate the latter once or twice a week due to some vacuum loss, but the chamber would not have needed an additional vacuuming so far. So, for now, I consider it ready for use and next week it will have some matter placed within it.

Thanks again for the help and suggestions. Oh, I will be removing the gauge I dropped in there as it will not register properly, but it will be no issue coupling a room temperature gauge as I do with my jars.
 
  • #47
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After nearly two weeks in the freezer, the vacuum in the chamber has not changed. I now feel confident using it for future projects. I did remove it from the freezer a day ago and the vacuum gauge I placed within it read correct levels once it warmed up. Apparently, the gauges are affected by the cold, so I'll know not to place it within the chamber in the future.

Thanks again for all those helpful suggestions and comments.
 
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  • #48
dlgoff
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Thanks again for all those helpful suggestions and comments.
I want to thank you for letting us know how it turned out. Nicely done thread, IMO.
 
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