Sciencemadness Discussion Board

How to secure glass stopcock; ptfe stopcock discussion

HoneySuckle - 6-6-2017 at 14:46

Glassware from China is so cheap, it's a crime NOT to buy it.

So I ordered a 1L sep funnel, and it came with a glass stopcock, secured by a rubber band. I went to the local chem/lab supply, looking for a ptfe stopcock to replace it, but they didn't seem to have the proper size.

Can anyone help me find my perfect stopcock? The current glass one has a "3" on it, which leads me to believe it is a 3mm bore. Diameter of the stopcock at the large end is about 15mm, and at the smaller end is about 12mm. Length of the plug section (the part that makes contact with the interior of the sep funnel valve) looks to be about 36mm.

I've had a tough time finding the ptfe version online. Since this glass stopcock came with only a rubber band securing it, I'd like to either replace it with ptfe/teflon, or find something to secure it other than the rubber band. The guy at the chem supply says that they are sometimes secured with metal clips. Anyone have experience with these clips and know where to get them?

Thanks,

[Edited on 6-6-2017 by HoneySuckle]

[Edited on 6-6-2017 by HoneySuckle]

Chemetix - 6-6-2017 at 15:28

Good luck with that....The taper on real glassware for taps is a 1 in 10 and the standard is exact. The chinese run the molds and grinding tools til they die, and a batch of the same product varies quite a lot. I've been given sep funnels to repair that have the key rocking badly in the barrel and never sealed from day one.

The same with the clips, they fit a standard, which has a very loose meaning when it comes to chinese manufacture.

HoneySuckle - 6-6-2017 at 15:42

Quote: Originally posted by Chemetix  


The same with the clips, they fit a standard, which has a very loose meaning when it comes to chinese manufacture.


Can you point me to the clips? I can't seem to find them anywhere.

Chemetix - 6-6-2017 at 16:21

As far as clips go...the only retaining devices that have any ability to be bought separately are the screw type

http://www.lenz-laborglas.de/en/stopcocks/1-way-stopcocks.ht...

buried in their catalogue is the spare taps and retainers


Lenzstopcocks.PNG - 203kB

These are the ones I'm used to working with...there are other suppliers out there.

[Edited on 7-6-2017 by Chemetix]

HoneySuckle - 6-6-2017 at 16:37

Think I found them here. http://chemglass.com/product_view.asp?pnr=CG-423

Any ideas as to the diameter of the sizes #1, #4, #5?

Magpie - 6-6-2017 at 17:30

I try to use glassware with the ptfe stopcock whenever possible. But I have bought clips like you show for the glass stopcock.

I tried to use a ptfe plug in a stopcock meant for a glass plug. It didn't work. IIRC it had something to do the glass surface being different: fire polish vs a fine grind. Also I'm not sure if the taper is the same. Maybe Chemetix knows.

Chemetix - 6-6-2017 at 17:40

Magpie is right, the surface is different. And the the taper is different for some manufactures than others, generally the Europeans and Americans use 1 in 10 but the length of the ground barrel varies, trying to get a spare key to fit an existing barrel is hard. It might fit the taper, but the hole won't align.

HoneySuckle - 6-6-2017 at 18:16

Quote: Originally posted by Chemetix  
It might fit the taper, but the hole won't align.


Yeah, this was my experience trying on various ptfe's at the lab supply store. Taper seemed right, but hole didn't line up/plug length was longer.

Dr.Bob - 6-6-2017 at 18:30

A few types of simple stopcocks are standardized, at least in America. In glass, there are #2, #4 as the most common, they have metal clips to hold them one, mostly. In PTFE, which uses a different taper angle, there are #2, #4, and #6 (big), the 2 & 4 are very common, Those are the standard ones, some vendors have other ones, like 3 ways, high vacuum, and other sizes, which are not interchangable in general. If you have Chemglass, Pyrex, Kimble, or most other US brands, they will use one of the 2 or 4 ones, most likely. No idea for Chinese ones.

US glass #2 = 10/13 mm and 30-31 mm length on taper

US glass #4 = 14/17 mm dia and 42 mm length on taper

I have never seen a #3 stopcock in glass in 30 years of chemistry. But the numbers seem consistent.

[Edited on 7-6-2017 by Dr.Bob]

[Edited on 7-6-2017 by Dr.Bob]