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FB receiving flask?
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DrugPhreak
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View Single Post5784
FB receiving flask?

 Mon May 30, 2005 9:59 pm		 Reply with quote
Would it be ok to use a FB receiving flask under moderate-high (29.5") vacuum? Or should the receiving flask be a RB also? The current fractional vacuum distillation will use a 125 or 250ml flask, but SWIDP is just wondering about this for when they scale up etc.
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joe_aldehyde
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View Single Post5785

 Mon May 30, 2005 10:06 pm		 Reply with quote
usually, duran erlenmeyers do just fine in such situations since your vacuum isn't really strong.
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Star-light
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View Single Post5788

 Mon May 30, 2005 10:39 pm		 Reply with quote
Quote:

usually, duran erlenmeyers do just fine in such situations since your vacuum isn't really strong


Maybe they do usually, but in general using a flat bottomed flask under distillation is a bad idea. Even if the vacuum is not really high then they are much more liable to implode than a RB flask. The same is true for both the distillation and receiving flasks.

A vacuum of 29.5 inches is almost 750mm of mercury. The pressure difference between the inside and outside of the flask is almost as much as when there is a complete vacuum inside the flask.

Of course there are FB flasks that are built for vacuum, but unless you have one of these then please avoid using them in a vacuum situation or you may end up in an accident.
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joe_aldehyde
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View Single Post5789

 Mon May 30, 2005 10:44 pm		 Reply with quote
750mm of mercury is 750 torr which is...only 10 torr less than atmospheric pressure! not a strong vacuum, right?
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DrugPhreak
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View Single Post5793

 Mon May 30, 2005 11:11 pm		 Reply with quote
This is the KNF pump I spoke about previously. It pulls 29.5" Hg (10mmHg). Thanks for the info.
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Star-light
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View Single Post5795

 Mon May 30, 2005 11:22 pm		 Reply with quote
joe_aldehyde wrote:
750mm of mercury is 750 torr which is...only 10 torr less than atmospheric pressure! not a strong vacuum, right?


Sorry Joe, by bad explanation. What I meant was the vacuum pulled was 750mm or the remaining pressure was 10mm Hg. Not a high vacuum, but too high for using standard FB flasks safely.

Oh, and DP, the bigger your flasks get the more danger you are in.
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DrugPhreak
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View Single Post5796

 Mon May 30, 2005 11:37 pm		 Reply with quote
So there's a chance of even a RB flask imploding if it's kind of large? Say like... 6 liters?
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Star-light
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View Single Post5797

 Mon May 30, 2005 11:59 pm		 Reply with quote
DrugPhreak wrote:
So there's a chance of even a RB flask imploding if it's kind of large? Say like... 6 liters?


I have never used a flask of that size under vacuum. I think it is generally recommended that you don't put flasks above 5L under vacuum, unless they have specifically been designed for vacuum use.

When using flasks above 1L it is a good idea to wrap the flask in fiber-reinforced ¾ inch friction tape to reduce the damage if one does break.

Always check a flask before using it and do not use a cracked, starred, or badly scratched flask as it is more likely to break.

Oh, and relieve your vacuum slowly to avoid sudden pressure changes which could cause breakage of the flasks. Do not relieve vacuum until the apparatus has cooled.
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DrugPhreak
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View Single Post5801
re: FB receiving flask?

 Tue May 31, 2005 2:44 am		 Reply with quote
Thanks for the info.
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loki
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View Single Post5817

 Tue May 31, 2005 8:34 am		 Reply with quote
definitely get heavywall pyrex rbfs, and there is ones you can get that have a special plastic coating that would reduce the danger in the case of an implosion, i'm not sure how much temperature they can take tho, depends on what the plastic is
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DrugPhreak
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View Single Post5864
re: FB receiving flask?

 Wed Jun 01, 2005 1:05 am		 Reply with quote
Yeah, some heavy wall flasks would be nice, but SWIDP is not planning on buying anything for while since they just spent a chunk-o-change on some equipment. Once you think you have everything you need there is always something else that comes up. SWIDP will be glad when they don't have to buy anything for a few years and just dream 24/7. Cool Shocked Smile
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