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
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
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.
