Sciencemadness Discussion Board

Leaking stopcock on addition funnel

Draeger - 20-4-2020 at 14:59

So, I have bought a used addition funnel from Ebay a while ago. Today, I used it again, but I noticed that reagent was flowing and dripping out of the side, where the other end of the stopcock is, and turning the stopcock to not let anything through sometimes doesn't really work, somehow. Sometimes, it just continues dripping on through.

So, I'm unsure what to do.

[Edited on 20-4-2020 by Draeger]

SWIM - 20-4-2020 at 15:24

Details please.
Is the valve core PTFE or glass?
Is the body the core goes in smooth or sort of a ground surface where the stopcock core contacts it?

The ground ones take a glass stopcock in almost all cases, and the smooth ones take PTFE.
Sometimes used funnels show up with the wrong core.
(I don't think I've got that backwards. Somebody pipe up if I did.)

Having the threaded nut tightened to the right degree on PTFE cores helps,there should be a little drag when you twist the valve.

But it may just be worn out or distorted a bit.

Is it your only piece of glassware with that sized valve core?

If you have a matching core in something else that works you can swap the cores to see if the core or the funnel is at fault.

If it turns out to be the core you can sometimes find unused ones on Ebay. New-old-stock.

I've had pretty good luck with buying used ones too. They usually work fine.
I think used ones are mostly from a funnel somebody broke while using, so the core is likely to be O.K.

EDIT: Oh yeah, and on Ebay you can always return it for a refund if it arrived in non-functioning condition. I think you've got 30 days.

The seller also might be willing to grant you a partial refund instead that is equivalent to the price of a stopcock core.



[Edited on 20-4-2020 by SWIM]

[Edited on 20-4-2020 by SWIM]

morganbw - 20-4-2020 at 15:32

Take the valve out and wipe it off. Put it back in and push to make sure it is inserted properly/seated. Tighten the nut.

Play around with what you can. You can make a good valve core leak if not careful.

Draeger - 20-4-2020 at 16:12

How do I remove the valve?

The valve is sort of like glass and it goes into a plastic sort of screw. I'm guessing that means it's a PTFE core.
I don't really know what you mean with body, though, but I can say what I have seen of the valve is all smooth.

mackolol - 21-4-2020 at 02:32

I have the same problem with my glass valve core. It's impossible to move when tight and if I loose it enough to make the addition work it often leaks.
It's pain in the ass, especially when I'm working with corrosive or toxic liquids, but I guess that it has just shitty valve, because I didn't have such problems with my previous one.
Maybe just try to cover it with grease or sulfuric acid before use to reduce the friction and tighten it more. Also see if the hole in valve core is fitting with the funnel when tighting.

wg48temp9 - 21-4-2020 at 03:12

Beg borrow or buy an intensely coloured lipstick. Lightly smear the conical surface of the plug with the lipstick. Reassemble the stopcock. Any gaps between the plug and barrel are shown by the intensity of the colour. Engineer's blue can also be used.

The same method can be used to check the fit of ground glass joints.

Draeger - 21-4-2020 at 04:22

Quote: Originally posted by wg48temp9  
Beg borrow or buy an intensely coloured lipstick. Lightly smear the conical surface of the plug with the lipstick. Reassemble the stopcock. Any gaps between the plug and barrel are shown by the intensity of the colour. Engineer's blue can also be used.

The same method can be used to check the fit of ground glass joints.

How do I disassemble the stopcock, though? Do I just pull the glass part out of the plastic part?

wg48temp9 - 21-4-2020 at 05:17

Quote: Originally posted by Draeger  
Quote: Originally posted by wg48temp9  
Beg borrow or buy an intensely coloured lipstick. Lightly smear the conical surface of the plug with the lipstick. Reassemble the stopcock. Any gaps between the plug and barrel are shown by the intensity of the colour. Engineer's blue can also be used.

The same method can be used to check the fit of ground glass joints.

How do I disassemble the stopcock, though? Do I just pull the glass part out of the plastic part?


I would think that could be determined by you looking at it. If not post a pic/pics so I/we can look at it and hopefully give you an informed answer.

Texium - 21-4-2020 at 07:09

Yeah it sounds like you might have some kind of unusual stopcock, so you’ll need to post a picture so that we know what you’re talking about.

In general though, ground glass stopcock always need to be greased. That is how they are designed. They don’t work without grease. Teflon stopcocks do not need grease. They should always fit perfectly and turn smoothly. As SWIM mentioned, the barrel of the stopcock will be frosted if it is meant to fit a ground glass valve, or smooth if it is meant to fit a Teflon valve. Typically, glass and Teflon valves are manufactured to different dimensions anyway though, so they’re generally not interchangeable.

Draeger - 21-4-2020 at 13:26


Here it is.

SWIM - 21-4-2020 at 13:54

That looks like a glass stopcock and the retainer looks like a knockoff of a Kimble/Chase stopcock retainer.

(But to be fair, for all I know the Kimble/Chase is a knockoff of somebody else.)

If I'm right, it looks like this when off the stopcock:https://www.amazon.com/Kimble-Chase-STOPCOCK-PLUG-Retainer/dp/B01N4KDARS

There's a part with a threaded end which is split into a few sections, and the outer part that just looks like a knurled threaded retainer threads onto this to squeeze it on the stopcock core shaft.

EDIT: sorry, wrong explanation. The part with the split threads should be held stationary and the threaded ring screwed as far away from the funnel as possible. This should release the split parts' grip on the stopcock core end so you can take it off.

I think... I'm going to look around and find one of those fittings. I know there are a couple around here somewhere.

https://www.amazon.com/Kimble-Chase-STOPCOCK-PLUG-Retainer/d...

Here's that picture as a link.






[Edited on 21-4-2020 by SWIM]

[Edited on 21-4-2020 by SWIM]

Texium - 21-4-2020 at 14:03

I can tell just from looking at that picture that it isn’t greased. You’ll need to take it apart and lightly grease the stopcock if you want it to stop leaking.