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smurf_master
Stranger Danger


Registered: 04/26/11
Posts: 449
Loc: Everywhere
Last seen: 4 years, 2 months
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Pc'd jar of water problems
#14729681 - 07/07/11 02:35 AM (13 years, 6 months ago) |
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When I go and PC a jar of water to make a syringe, I have trouble sucking out anything but air from the jar. What am I doing wrong? Using a single rtv silicone hole. Should I crack open the lids to let the pressure out, that would seem to defeat the purpose.
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SB-2
Innovator




Registered: 10/18/10
Posts: 159
Loc: Between Here and There
Last seen: 6 years, 2 months
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Remember science class in elementary school?
Air expands/contracts with temperature. As it heats up, it expands, and as it cools, it contracts. Since you used just silicone and nothing to allow for gas exchange, the hot air in your atmospherically sealed jar contracted as it cooled down, creating a strong vacuum inside the jar. Does the plunger try to slide back in as you draw water out? If so, you have a vacuum fighting you and that is your problem.
The easiest solution requiring no extra materials would be drawing air in from inside a flame (Alcohol flame is best), then aspirating the air into the jar to equalize the pressure.
The best solution is using a filter for gas exchange, but if you want to be able to shake/turn upside down/etc, I like Evenflo baby bottles with the nipples inverted and filled with silicone. You'll run into the same problem with the vacuum issue, but they sure are easy to work with.
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mr_squee
the noobiest

Registered: 04/09/11
Posts: 82
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Re: Pc'd jar of water problems [Re: SB-2]
#14729966 - 07/07/11 06:25 AM (13 years, 6 months ago) |
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Strictly speaking, if your jars were sealed when they went in the pc there won't be a vacuum once they've cooled. The heating will cause positive pressure inside the jar which will not escape if the jar is airtight. As it cools the pressure differential will decrease as the jar approaches the temp (room temp) at which you originally sealed it.
It is likely that you can't aspirate anything out because there is nowhere for air to go in (and fill the space) as you remove the liquid. The air you are seeing 'sucked out' is likely to be leaking in from the air around the seal on the plunger rather than coming from inside the jar.
You need a way for filtered air to get in as you suck liquid out. I use a 1/4" hole covered with a square of tyvek sealed with micropore tape on both sides which works well. If you really want to use that jar then get another syringe, take the plunger out, put some ipa soaked cotton balls or polyfil in it and push the needle through your injection port. Then go ahead and aspirate through your original syringe. Air will be sucked in the second syringe but will be filtered through the ipa soaked cotton/polyfil.
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