lullu - 7-10-2014 at 10:59
Is there any easy trick to reduce gas output in a cost friendly way when using a normal apparature used for welding?
Something around 1l/minute is the minimal setting on mine which is way too much.
forgottenpassword - 7-10-2014 at 11:17
Hoffman clamp.
Dr.Bob - 7-10-2014 at 12:04
Just put a needle valve somewhere in the line, preferably right at the regulator. They are not hard to find, Swadgelock makes good ones, but there
are many sources. I often have my N2 at only a bubble per few seconds for overnight reactions, that may be low for during handling reactions, but it
does not consume much gas.
lullu - 7-10-2014 at 12:11
Thank you, another question do you guys use a back pressure valve or just a drying tube on the end?
Do you measure the bubbles by letting it thru water after a washbottle to prevent suckbacks?
jock88 - 7-10-2014 at 13:59
Where can you get precision needle valves? The needle valves you see on ebay are not very 'needle like' as the 'needle' is really just a blunt end
shaped at 45 degree.
I had alway thought the a proper needle valve has quite a long needle type structure that went down into a hole and you had to make (say) 20 turns to
go from top to bottom of the range. Or am I looking for something that does not exist.
Quite a beast here:
http://www.ebay.co.uk/itm/GAUGE-VALVE-4000-PSI-PRECISION-AJU...
Dr.Bob - 8-10-2014 at 05:45
When I search for "swadgelok needle valve" in Ebay, I see 414 hits, many of which are $9.99 or so. The real challenge is finding the right tubing
and connectors, simplest is to use NPT connectors, most of those are available at Home Despot. If anyone wants some and is patient, I could likely
find a few, with tubing and connectors, in my boxes of random stuff, but it would take a little while, and I would need to know the input and outputs
needed.
As for the bubbler, I use an oil bubbler, with 1 - 3 inches of oil, depending on the design. Water is NOT a good choice. Make sure that there is a
trap, enough tubing or a design that prevents back flow, in case you create a partial vacuum, or you will suck the oil into your reaction. Having a
small outlet on the bubbler does help create a slight inert pressure, but you have to be careful to not create more than a few psi, or things tend to
pop apart.
Magpie - 8-10-2014 at 07:43
I use a small gas rotameter calibrated in L/min. I have rubber tubing so as Dr Bob says this can pop off if my regulator pressure is too high.
nannah - 9-10-2014 at 10:56
Can you really use welding grade N2 or Argon? I have been reading alot lately about solvent drying, and i am thinking about maybe buying some gas in
the future.
I must say that i also appreciate the tips in this thread.
Thanks.
Dr.Bob - 9-10-2014 at 11:56
If you use lower grade gases, the main thing is to put a drying tube in the line somewhere. But 99% nitrogen or argon is still much better than air,
and even the worst inert gases are likely better than that. The key in that case is to not flow the gas through the reaction too fast, as then any
small impurity will react faster with the reaction. You just want to displace the air that was in the flask and then keep a slight positive pressure,
then you will have little gas flow and any impurities in the gas will be used up quickly, if they react with your chemicals. For any reaction the key
is what compounds do you need to keep out, for most reactions, water is the main issue, for some oxygen, for Grigyards any CO2 is bad but also O2 and
water, and for some chemistry any trace of nearly anything is bad (some Pt catalysts, Ni(COD), Lithium, KH, etc). But for much chemistry, plain air
is fine, or just N2.