I have a 19/22 Kontes 125 mL pressure equalizing funnel that I would dearly like to be able to use. The problem is that it has no plug for the
stopcock.
The reason I can't just buy one from US vendors is that it has a 1:10 taper instead of the 1:5 taper of the US standard stopcocks. I assume it
originally came with a glass plug, which is available in the 1:10 taper.
But I really want a Teflon plug. This is available in both Germany and the UK. I have contacted their US distributors, and they in turn have
contacted their German and UK distributors. However, they won't sell just one piece.
So, I'm asking for help. Hopefully one of you will have a plan for how I can get a teflon plug.
[Edited on 16-10-2009 by Magpie]densest - 15-10-2009 at 16:54
If all else fails, do you know someone with a lathe? Turning such a taper in Teflon is pretty easy assuming very sharp tools and a steady machine. A
very small lathe would work. It would be small enough that someone in another country could mail it to you, right? What are the necessary dimensions? entropy51 - 15-10-2009 at 17:08
It's possible to machine a taper from teflon on a small lathe. I have machined 24/40 joints from teflon, but as densest suggests it's not especially
easy. Someone who's better than I am on a lathe could probably turn one out for you. I'll bet someone here could do it.panziandi - 15-10-2009 at 17:24
Contact me through U2U I can give you the contact details for a glassblower in the UK who, if you email with the request, details etc, maybe able to
sort you out with the correct part and send you. No idea of the costs involved.watson.fawkes - 15-10-2009 at 17:25
I believe I recall seeing these in the catalog of one of the suppliers to glass fabricators, but I can't recall which one it was offhand. A call to Pegasus Glass (they sell lampworking blanks) couldn't hurt, though.Magpie - 15-10-2009 at 17:27
Yes, I do know a carpenter with a lathe. In, fact he turned down a 1" (25mm) wood dowel for me this summer to a 24/40 inner taper (1:10).
I also contacted Kimble-Kontes but they could not help me.
I will get the German and UK specifications and post themMagpie - 15-10-2009 at 17:41
[Edited on 16-10-2009 by Magpie]Sedit - 15-10-2009 at 18:46
Just a suggestion for you, I have performed simular feats before using a dremel tool as the lathe on small wooden items. You would need to find a
bolt that fits nicely into the dremel and a threed on it that will tighten as its turning to make sure the nut does not fly off. Clamp the dremel to a
table and put the bolt thru the object to be worked(im assuming it will need a hole thru it anyway)and lathe away. You may not want to do all of this
but it does work well for small objects like knobs for cabinet and such so I can't see how it would not work here as well.
[Edited on 16-10-2009 by Sedit]1281371269 - 16-10-2009 at 09:54
It's going to be difficult to turn teflon on a wood lathe due to chucking issues and accuracy difficulties. I think you'd need a precision mechanical
lathe. But if all else fails, you could cover the wooden piece you have with teflon tape which would work until you got a better piece.Magpie - 16-10-2009 at 10:08
Yes, I'm not too hot on the lathe idea. Although I could buy an oversize US piece with the 1:5 taper and have a machine shop put a 1:10 taper on it.
This sounds like an expensive and overly complicated way to go, however.
The wood dowel with 24/40 inner joint (taper 1:10) is a different size for a different project.
I really just want to buy a UK or German plug.
UnintentionalChaos - 16-10-2009 at 15:04
Is the inside of the stopcock part ground or fire-polished? You're not really supposed to use teflon plugs on ground joints, as the seal won't be
quite as good.
I've gone looking for even a standard size teflon stopcock plug, and found it exceptionally hard to buy.
EDIT: fixed some of my own engrish.
[Edited on 10-17-09 by UnintentionalChaos]Magpie - 16-10-2009 at 15:51
Quote:
Is the inside of the stopcock part ground or fire-polished? You're not really supposed to use teflon plugs on ground joints, as the seal won't be
quite as well.
Very good point! The inside is ground glass! I hadn't noticed that difference. I think I will buy a glass plug and give it a try.
Teflon plugs (1:5 taper) can be bought here for those in the US:
I never knew that magpie. I guess it makes sense though. I guess I thought of it but never thought it would be bad enough to cause a leak.UnintentionalChaos - 17-10-2009 at 08:52
I never knew that magpie. I guess it makes sense though. I guess I thought of it but never thought it would be bad enough to cause a leak.
Well, teflon lubricates poorly against a rough surface, first of all. It's at it's best against hard, smooth surfaces. Compare rubbing your finger and
rubbing a piece of polished steel against a piece of teflon.
I suppose that over time, the teflon will wear off and "level" the ground portion, but in the meantime, the joint won't rotate as well as it could. It
may also be an issue if you want to pull a good vaccum on the system.Magpie - 24-12-2009 at 13:55
This is just a repeat request as I'm still seeking an archaic glass stopcock plug for a pressure equalizing addition funnel. The size is 10/25, with
2mm bore. Kontes lists it in their catalog but they do not stock it.
It is part no. 305751-0221. Any help in finding one would be greatly appreciated. vulture - 24-12-2009 at 14:15
Is this the piece that is used to control flow in extraction funnels, columns, addition funnels and two way valves?
And what exactly is taper? Is it the ratio of decrease of thickness? Magpie - 24-12-2009 at 14:28
Vulture, I'm just not sure where else this small stopcock is used. On the stopcock body itself it has the designation 2-A.
My understanding of taper is that it is = (D-d):L, where D=large diameter, d = small diameter, and L = the distance between the two diameter
measurements.
In the US the glass stopcocks seem to all have taper of 1:10 whereas the PTFE stopcocks all have 1:5 taper. In Europe it seems that PTFE stopcocks
are 1:10.
This is just a repeat request as I'm still seeking an archaic glass stopcock plug for a pressure equalizing addition funnel. The size is 10/25, with
2mm bore. Kontes lists it in their catalog but they do not stock it.
The designation 10/25 means that the diameter at the bore hole is 10mm and the length of the stopcock ground portion is 25mm. So it doesn't look like
Wilmad has one, unfortunately..vulture - 1-1-2010 at 02:44
I might be able to acquire a few of these for free if I can figure out the right dimensions. We'd have to arrange something for shipping then.
The pain with using glass in valve applications is that you need lubrication, which tends to contaminate your product with lubricant.
[Edited on 1-1-2010 by vulture]densest - 1-1-2010 at 13:15
@magpie - are you -sure- of the 10mm and 25mm dimensions? It seems strange that a big manufacturer would use a non-standard stopcock... maybe put some
modeling clay or other soft equivalent in the bore so you can use a set of measuring calipers at the points mentioned in the Wilmad catalog excerpt?
A wild guess would make it a #1 1/2 or a #2......... Magpie - 1-1-2010 at 17:19
@magpie - are you -sure- of the 10mm and 25mm dimensions? It seems strange that a big manufacturer would use a non-standard stopcock...
I agree, but take a look at:
http://208.72.236.210/html/pg-634500.html
Here Kontes has several funnels that they say use the 305751-0221 replacement plug. But when you contact them they don't have the plug.
I've taken my own measurements with inside calipers and they are consistent with the 10/25 of 305751-0221.
Vulture, thanks for the offer of help. I do agree about the grease contaminant issue. I just hate to throw away this expensive piece of glassware
for want of a stopcock plug.densest - 1-1-2010 at 18:40
Have you checked the used lab equipment places like the one in Maryland or the couple of glass people in Pennsylvania? I've gotten a number of
miscellaneous parts from them over the years. Otherwise, turning glass on a lathe with a turret grinder isn't too hard. I guess the taper and the
diameter at the bore fully define the desired piece....
I can PM the urls for the equipment places; I'm not sure I want the whole of scimad to descend on them at once - all the good stuff would get sold before I can save enough to buy it!
I checked my "junk glass" box - no luck
Two or three supply houses on the web have the item in their web ordering pages - you've probably gotten the "no stock, sorry" answer from them too.
- all the good stuff would get sold before I can save enough to buy it!