teflon stopcock replacement for glass stopcock

[grandpa]

Simple question,

Swim bought a separatory funnel with a glass stopcock and would like to know if it can be replaced with a teflon stopcock, without leaking?

[abolt]

If it is of the same dimensions then I don't see why not.

Teflon "stopcocks" usually have rubber "O" rings to assist with sealing the apparatus anyway.

[biotechdude]

Use a little plumbers tape to make it snug.

[hest]

ass long as it's tight it will work. Plastic, teflon, methal rubber ect works just fine. (actual my hand work's and it don't even fit into the hole)

[mr_pyrex]

Actually you might be able to get it to work...but they are two different types and are NOT interchangable for all intents and purposes.  If you wanted teflon you should have ordered teflon otherwise I'd recommend sticking with glass ground and just use a good silicone based lube for the stopcock as it is least likely to interact with most of the commonly used substances around here.  And someone mentioned rubber orings being used along with teflon...that is entirely possible, however think about it....what is the purpose of the teflon in the first place...to use it without the need for anything else and to be inert towards the usual substances....an o-ring added to a telfon stopcock is kinda self-defeating.  Anyways do whatever you feel works for you but to answer the question, no they are NOT readily interchangable and should be kept the way they were designed.  Pyrex out of stoppers ;-)

[Osmium]

> Actually you might be able to get it to work...

Funny, all my sep funnels were made for glass stopcocks and use teflon now.

> If you wanted teflon you should have ordered teflon otherwise
> I'd recommend sticking with glass ground and just use a good
> silicone based lube for the stopcock

I disagree.

> an o-ring added to a telfon stopcock is kinda self-defeating


I wonder how you want to make the stopcock work without an o ring?

[ApprenticeCook]

i bought replacement stopcocks for my funnels... easy as ring up and order the bore size...
Came in a neat little pack with o rings and screw seals, fitted perfectly.

[Rhodium]

Teflon Tape: The Leaky Buret Remedy
Brett C. Boshco and John J. Griffin,
Journal of Chemical Education 77(10), 1342 (2000)

Burets used by high school and college students for classical titrations may be purchased with three separate interconnecting components consisting of the main glass stem, a stopcock (usually made primarily out of Teflon), and a replaceable glass capillary tip. The replaceable glass tip makes the three-component buret more attractive than the unibodyconstructed buret, which may become permanently inoperable if the capillary tip becomes clogged with grease, dirt, or soap powder. Ironically, replacement of these tips may prove to be quite challenging owing to variations in the external diameter of the replacement glass tips. These diameter variations are frequently the cause of leaks and they prevent the buret from being used effectively. In many cases, the application of silicone grease proved to be inadequate in correcting leaks. As a remedy for buret leaks caused by an improper tip-to-stopcock fit, Teflon tape (1.2 cm in width), available in most hardware stores, should be wrapped tightly around the glass tip before it is inserted into the buret’s stopcock. When inserting the glass tip into the stopcock, rotate the glass tip in the direction opposite to the direction in which the tape is wrapped around the glass. The Teflon tape will fill voids as the glass tip is pushed up into the stopcock, providing the seal needed where silicone grease failed.

[mr_pyrex]

If your stopcock can't work without a o-ring I would think you have a more serious problem then maybe just converting it or trying to replace the stopcock alone.  Like maybe the equipment has too much wear and tear on it and should be replaced with new equipment.  I mean I'm looking at the Fisher catalog as we speak and none of the Pfte stopcock funnels or even the glass ground joint funnels shown has ANY o-ring included in its assembly.  There is only two parts needed for a glass setup 1)the stopcock 2)the springloaded lock clip and three parts needed for the teflon assy-1)the stopcock  2)the teflon washer  3)the teflon nut.
  So if your using equipment that has o-rings, maybe it is time to get new updated equipment.   And if you have a glass stopcock that is unable to seal with silicone grease alone...again updating your worn equipment would be a wise investment.  Pyrex out of catalogs ;-)

[Osmium]

Where I come from the O ring is placed between the washer and the nut (which aren't made from teflon). No springs being used for stopcocks, that's what the O ring is for. It doesn't come into contact with any chemicals, it just pulls the stopcock into its seat when you tighten the nut.