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Author: Subject: My teflon stopcock is leaking, is there anyway to fix this?
alking
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[*] posted on 30-3-2016 at 07:00
My teflon stopcock is leaking, is there anyway to fix this?


So I just noticed today there is a small leak on my sep funnel's stopcock. I thought I noticed it before but wasn't sure until I left a solution in it overnight to find a puddle down below and staining along the side. It's my understanding that you grease glass stopcocks and teflon ones are simply supposed to work, however mine seems poorly manufactured. Am I sol or is there something I can do? I can't seem to get it out to actually apply grease, but I'm hoping maybe there's some tricks I haven't picked up yet.
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Magpie
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[*] posted on 30-3-2016 at 08:37


You should be able to disassemble the stopcock easily. I usually disassemble mine after using so everything can be easily cleaned. When reassembling I leave it loosely assembled for storage. I tighten it appropriately just before use.

I bought a used Pyrex 125 ml separatory funnel off eBay. It leaked. I replaced the teflon stopcock with a spare I had on hand. It works well now and doesn't leak.




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Loptr
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[*] posted on 30-3-2016 at 10:06


I have a few different brands of separatory funnels, and they typically come with instructions of how to prepare them for use. The set of instructions that I can recall says to not grease it, but to start off with a very thorough cleaning with a solvent followed a sort-of wearing down of the stopcock by rotating it within the glassware's stopcock hole until there is a very snug fit. I thought it was snug enough to begin with, but I have noticed that DCM solutions have noticeably leaked out over the course of a day or so. I assume this is due to the density of DCM, and would imagine something like bromine would be even worse.

I believe those instructions were for a Pyrex separatory funnel.

[Edited on 30-3-2016 by Loptr]
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[*] posted on 30-3-2016 at 14:04


1) no you never grease a ptfe stopcock. The point of using ptfe is to *avoid* greasing. 2) you shouldn't leave a sep funnel overnight with contents in it. 3) if you must leave contents in the apparatus at least put a beaker under it. Reagents cost more and more every year. It's a shame to waste them this way.

Were you trying to "wait out" an emulsion? I do this for that reason and pretty much only that reason. Sometimes vibration and/or washing with saturated NaCl solution can help break up an emulsion.

Since this new to you, disassemble the apparatus, clean it well including the stopcock, check the "O" rings and replace if indicated. Indicated by obvious wear, compression, ugliness, etc.
Re-assemble and check that t doesn't leak in an obvious manner. Overnight small puddles don't count. Always have some sort of vessel under the funnel and leave the stopper out except during active use such as running an extraction or washing a solution.

[Edited on 30-3-2016 by chemrox]




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organicchemist25
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[*] posted on 30-3-2016 at 18:35


I had the same issue with a PTFE stopcock. It must have been defective in sizing or had maybe a damaged spot on it. I just ordered another one and it works great. Definitely think a new stopcock should fix it. If not, it would have to be the cone shape is defective in the sep funnel itself.
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[*] posted on 30-3-2016 at 18:37


I had the same issue with a PTFE stopcock. It must have been defective in sizing or had maybe a damaged spot on it. I just ordered another one and it works great. Definitely think a new stopcock should fix it. If not, it would have to be the cone shape is defective in the sep funnel itself.
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[*] posted on 31-3-2016 at 08:58


Yeah, I'm thinking it might just be defective and could use a replacement. I did not know it was bad pactrice to leave a solution in a sep funnel, but I will keep that in mind for the future, I want to take care of my equipment. Mine had no instructions, it was an ebay purchase from china, new, but sometimes the quality is lacking and this may be one of those cases. I can tighten it to the point it's hard to turn and it still leaks. I'll see if I can dissassemble and clean it or failing that replace it to ressolve the issue. DCM is actually the first thing I noticed leaking in it as well, some time ago, but had not noticed a problem with other solvents until this event, or at least significant enough to realize it was a leak as opposed to a spill. Fortunately this was just methanol so nothing particularly toxic or valuable, and only a few ml at that I would wager. Btw, why is it a bad practice to keep the glass stopper in it when not in use?
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