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watson.fawkes
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[*] posted on 17-11-2008 at 21:09


This BBS software mangles raw URL (particularly annoying with attachments). Anyway, that eBay auction is still there; just can't click on the auto-generated link. Use this one:<br>http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=370112174805
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Sauron
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[*] posted on 17-11-2008 at 21:27


As the auction is completed the entry is now only viewable by buyer and seller. Anyway the item description is unequivocal:

BUCHI Rotavapor M with HB140 Waterbath + glassware BNIB

I have what I think is a complete set of Buchi brochures, exploded drawing and parts lists and I have never heard of a Model M nor of a HB140 water bath. That does not mean that the description is wrong. I am willing to concede that there is a slim possibility that a model has eluded my attention. I will ask the Buchi agent. That's where I get my old Buchi tech material.

Okay this is a micro Buchi that I never heard of before, and no longer made. However there is a very good chance they will still have spares and glass, check with the UK agent to be sure.

If the max flask size is 250 ml you need to be aware that you are not to fill the flask fore than 1/3 to 1/2 (ar most) so with this model you are constrained to 80-125 ml sample sizes. That is 1/10th the capacity of the normal benchtop Buchi that handles 1500 ml in a 3 L flask.

Anyway good luck with your purchase. Older Buchis sans printed circuit boards tend to last forever, short of a major seal failure while stripping something mega-corrosive.

[Edited on 18-11-2008 by Sauron]




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DJF90
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[*] posted on 18-11-2008 at 08:58


As far into the future as I can see it should only be stripping off solvents. If I can get a vapor trap to operate at ~-30 (salt ice bath with CaCl2.6H2O), then would this be enough to stop the solvent vapors entering the pump? Should just be stuff like Et20, DCM, AcMe, and maybe toluene (so long as I can get hold of them).
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Sauron
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[*] posted on 18-11-2008 at 09:37


No, -30 C is not adequate for Et2O and maybe not DCM if youyou are looking to protect your pump oil in a 2-stage pump. Figure out the bp of these at say 10-20 torr to see why.

That is why a pump impervious to solvent vapors is much preferred for rotavap work. Aspirator or PTFE diaphragm only. Aspirator is cheaper. Then comes recirculating dual aspirator, then the PTFE diaphragm pumps are costliest in this class.




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[*] posted on 18-11-2008 at 10:06


Ok i got it. Bp (Et2O) at 15 torr is -45C ish. But... we never strip of ether at 15 torr in the lab, more likely 450 torr. That way it just about condenses at room temp (~20C). A SS needle valve could be used to moderate the vacuum to ensure that the ether will condense at room temp under said vacuum? And then I need to measure the pressure somehow, maybe I can find a gauge that gives absolute pressure in torr.

EDIT: Don't worry, I really should stop clutching at straws. I think I dont really have much choice under my circumstances but to go with the vacuum aspirator. Plus it'll be better off in the long run. Thanks for you're help Sauron, and thanks for being so patient with me.

[Edited on 18-11-2008 by DJF90]
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Sauron
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[*] posted on 18-11-2008 at 10:47


The temp of the coolant has to be substantially lower than the bp of the solvent at the vacuum in question, remember. At least 20 C. lower. This is a hard lesson to learn if you have to rebuild your 2-stage pump or even just do an oil change. I can tell you, even N2 and CO2/acetone traps are not perfect.

Anyway, you will find out for yourself.




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[*] posted on 18-11-2008 at 13:32


I appreciate the input Sauron. I will read up on the relevant threads at the next convenient time. Thanks again
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Sauron
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[*] posted on 18-11-2008 at 21:53


The problem with using the needle valve/controlled leak technique instead of a real vacuum controller is that you are introducing air into the system, and in many instances the product neds to be carefully isolated from the air.

So unless your needle valve is hooked up to a N2 or Ar cylinder with a regulator than can tolerate the pressure differential between the compressed gas on one side and the partial vacuum on the other...

Aside from that, once most of the low boiling solvent is stripped you will have solvent condensed in receiver and when the vacuum is increased it will start to boil in the receiver. I have seen it happen. This can overload the condenser. Buchi now recommends a secondary condenser to reduce solvent getting to the aspirator for green purposes.




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[*] posted on 19-11-2008 at 05:08


Sorry I didnt mean an air leak. My idea was to just put a SS needle valve in between the vacuum pump and the apparatus, and only open it up enough to get required vacuum. I suppose now this wont work because if there is some way the apparatus can get evacuated, whether its a regular sized bore or a tiny little gap in the valve, it will be evacuated to the unltimate vacuum of the pump.

If an air leak is included then surely any air that leaks in will get sucked into the pump (so long as the leak valve is between the apparatus and the pump, preferably closer to the pump?
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[*] posted on 18-12-2008 at 00:19


I was not expecting this Cole Parmer item till mid January but they surprised me.

The brass assembly consists of six pipe fittings screwed together:

A CGA320 hex nut and 2 inch long double ended 1/8 MNPT nippe with a sealing washer and a hex nut to retain the CGA nutscrewed into a 45 degree elbow and a reducer 1/8 NPTM x 3/8 NPTF end, mating to the "nozzle" which appears to be simply a 3/8 NPTM plug which has been drilled with a small hole to pass the liquid CO2 from cylinder with a dip tube and valve. All off the shelf except for the hole in the "nozzle". Maybe $10 worth of ordinary hardware.

The nozzle and a few washers retain a plastic cone which is where the PE collector bag attaches via a plastic ring and a very ordinary hose clamp. At $150 someone is making a killing with this.

The nozzle hole I have not yet measured but I would guess 1/8 to 3/32 inch at most and I doubt this is critical.

I will report back after trying this out next week, time to order a couple cylinders of CO2 with dip tubes.

The fittings are all off the shelf except Swagelok does not seem to have the 45 degree elbows at all. Just 90 degrees.

I am sure other pipe fitting suppliers will have it.

I will see about making a bill of materials in case anyone wants to assemble one of these DIY and save a bundle.

I just ordered (from local supplier for immediate delivery) a 6Q cylinder of CO2 w/valve and dip tube for $175 (I then own the cylinder and valve, refills are very cheap.)

A 1.5Q same would be $60



[Edited on 19-12-2008 by Sauron]




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Sauron
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[*] posted on 19-12-2008 at 05:26


I received the first 6 m3 liquid CO2 cylinder (48 liters) with brass CGA320 valve and safety cap today, I purchased the cylinder new (rather than paying drayage) for $175 filled, locally, including required dip tube. Refills are very cheap, so the cyl and valve and Frigimat are one time costs.

I tested it, it works, well but noisily with a loud industrial shriek.

I am quite pleased and regard this on-demand system of dry ice flakes as far superior to buying slabs of dry ice which never get to slurriable form.

PlasLabs/Scienceware wants too much for this accessory, but I can list all the bits and pieces and anyone can put this together even if not DIY-inclined. It's all off the shelf with very slight modifications. A welding supply, and any hardware store are all you need and some scrounging for an appropriate plastic cone.

ou need

Assy 1

-- a CGA320 brass regulator cap and nipple, 1/4"
NPTM A hex nut is flush at one end of regulator nipple and a nylon sealing washer is used between valve outlet and regulator cap.A CGA320 sealing gasket (washer)

Put those together and you have a nonrotating pipe nipple for CGA 320 valve

Assy 2

A 45 degree brass elbow 1/4 NPTF both faces.

A reducing adapter 1/4 NPTM x 3/8 NPTF brass

A 3/8 NPTM plug brass drilled through 1/8 inch

Put those together and you completed the pipe fittings

Plastic cone

This is a small plastic drinking glass drilled at base to be retained by the brass plug and a flat washer. Another flat washer is on inside. A snapon ratchet wrench with extension socket will be hady tightening this up.

You will need appropriate bags to contain the dry ice flakes as formed and a hose clamp ortwo to retain them on cone.

The correct valve opening is THREE QUARTERS of A TURN no more no less. Some hapless jerk decided this meant three or four turns and ended up in hospital with liquid CO2 burns all over him.

When not in use I remove the Frigimat and replace the cylinder cap which protects the valve in case of a fall. A cylinder stand is good idea, buy or build one.

Photo below is CGA320 regulator cap and nipple including the required hex nut. Nylon washer not shown.

[Edited on 20-12-2008 by Sauron]

3-7584.jpg - 5kB




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[*] posted on 19-12-2008 at 11:46


I just got my first christmas gift from school today, a beautiful Mettler H54AR 160g d=0.01mg (that's 5 zero after the dot :D). Still need to make it work, it seem to have too much weight in the back part thus it's always off limit, i'll work on that during the vacation.



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Sauron
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[*] posted on 21-12-2008 at 21:04


I have the Swagelok part numbers for the reducing fitting, plug, and elbow if anyone wants them. In Thailand the Swagelock agent want 800 baht for these 3 items all together ($24), Doubtless they are less in USA.

Swagelok does not sell the CGA320 regulator cap and regulator nipple w/hex nut and nylon washer, but these are easy to find from welding suppliers. In fact I just called my gas shop and they have the correct cap, nipple and nylon washer in stock, price 200 baht (< $6 US).

While Swagelok quality is super, the rest of these fittings (plug, reducer, and elbow) are just hardware store brass gas pipe fittings and without a doubt cheaper at such places than from Swagelok.

-------------------

This standard CGA320 regulator nut and nipple: nipple turns out to be 3/8 NPTM somewhat longer and beefier than the 1/4" NPTM of the Frigimat Jr. So, I will replace the 1/4" NPT female elbow with a 3/8" NPT one, and the nozzle (plug with a 1/8" hole drilled through by me) can screw into that directly, no reducer required. So my DIY "Frigimat Jr" clone will not look exactly same but it will work exactly same as the $150 original.

When I have it all together I will post a pic. It'll be a day or so while I get the Swagelok bits in.


[Edited on 22-12-2008 by Sauron]

[Edited on 22-12-2008 by Sauron]

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