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watson.fawkes
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Quote: Originally posted by not_important  | | It's not just the exothermic nature, it's that the SO3 tends to form fine droplets of H2SO4 that are difficult to collect or absorb into dilute acid
or water[...] |
Yes. There are any number of reasons not to use dilute water. My immediate concern in
explanation was to point out that absorption in dilute water would likely melt a small filter pump.
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james1956
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i took a brass firehose nozzle [ about 6''] that fits on a garden hose, drilled a 1/4" dia. hole at a 45 degree angle. inserted a slightly curved
piece of 1/4" copper, soldered it in. put a 3' piece of galv. steel pipe with a 90 and a valve , put in a tote filled with water. works great.
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entropy51
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Welcome james 1956. That was a good year (I can sort of remember it.)
You made an aspirator and it worked on the first try? Impressive. I tried to make one a time or two, gave up and bought one.
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elementcollector1
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I can't seem to get my aspirator to work. I've plugged it in the right way, with a garden-hose brass barb connector (same as you'd find on the average
condenser), but no matter how high I turn the water up, the filter doesn't run any faster. Does anyone know why this is? My guess is that I need a
larger diameter input of water (i.e. not using the barb, but rather connecting to the hose directly somehow).
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bfesser
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In my experience, a filter will only run so fast, no matter how hard a vacuum you apply. What make/model of aspirator are you using? Have you taken
a pressure reading on your water supply?
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MichiganMadScientist
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My following suggestions are very half-assed, but in the absence of other options, they work:
If you need vacuum, you can purchase a hand pump vacuum brake bleeder system from your local auto parts store. It will produce enough vacuum for
vacuum filtration, and even for Some vacuum distillation applications.
If you need a water aspirator to circulate water through a condenser, a simple siphon getup should work.
Again, these are desperate measures, but they work if your lab happens to be located in a room with no plumbing..
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elementcollector1
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I guess I'll go to the hardware store and see if they can get me a brass fitting that connects to the aspirator itself.
Hand pumps, as I've been told, are faulty and unreliable. Not sure why.
My lab is located in the garage, and it's easy to run a hose around through the garage door. Where's yours, MMS?
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bfesser
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No
answers?
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elementcollector1
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My mistake, forgot about that part. Model is, as I can tell, Bel-Art Scienceware #329470000 (bought here: http://www.amazon.com/Bel-Art-Scienceware-329470000-Polyethy...)
Now, the next thing I should do is figure out the hose size and tank pressure, to determine the maximum pressure this is capable of putting out.
(What I should really do is buy a strong water pump...)
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bfesser
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Do you have a gauge to test your household water pressure? (0 – 40 psi / 275.8 kPa)
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elementcollector1
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Parents claim 60 psi, which doesn't seem right. Is there a standard for American households?
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elementcollector1
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Heh. Evidently, I am an idiot when it comes to vacuum testing. I had recently bought an aquarium pump which claimed 110 GPH, and for all I know lives
up to the claim. However, upon attaching to the aspirator, it failed to do anything. My setup for testing vacuum was simple: A pear-shaped flask with
one 14/20 joint and one glass tube (for hose connections). The tube was connected by vinyl tubing to the aspirator outlet. The 14/20 joint was
connected to a vacuum gauge I had bought in the same order (which is strangely stuck at ~5 in. Hg). The fit between the gauge and the ground glass
joint was a little loose, so I used tape (such scientific apparatus!) to fix that. The apparatus was for all intents and purposes air- and
water-tight. Worked perfectly. Upon testing with the aquarium pump, the needle never even moved.
Upon testing with the garden hose outlet (which I had earlier discarded as being 'too weak', due to the fact that my finger wasn't being sucked inside
when I blocked the outlet), the vacuum pulled was at least 25 in. Hg! I was hesitant to try further, as I might either break the gauge or the
glassware (it's ChemLab brand, if I recall, bought from Dr. Bob a while back). The gauge was maxed out at 25 in. Hg due to the +5 reading mentioned
earlier, so I'm not sure what it would do. If about 30 in. Hg is absolute vacuum, I might actually fix the gauge by pulling it past maximum,
as when the vacuum was broken the gauge would just drop back down accordingly.
Sorry for the confused jumble of thoughts, I just wanted to report the success with the garden hose to those of us who are interested in home vacuum.
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Dr.Bob
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Just a note, most water aspirators have a built in ball check valve, that tries to prevents water from being sucked into the vacuum line, but they are
notorious for getting stuck, so often just shaking the thing until you hear the ball rattling inside is all that it takes. Or, if you have clogged
the poor things with sludge, some of them can be taken apart and the valve space cleaned with a q-tip or cotton swab or needle. PS, I recently found
a brand new plastic aspirator from Nalgene that looks just like the one in element collector1's post, they are decent, but maybe not the best ones
ever made, I personally prefer the metal ones, but they corrode easily. It would be $5 plus postage if anyone wants one.
And normal water pressures in the USA range from 40 (very low side) to over 100 psi (quite high, but ideal for showers) so the 60-80 would be pretty
normal. Many new houses have pressure regulators built in, along with one way check valves, which can lower the pressure, too much in some cases.
[Edited on 17-4-2014 by Dr.Bob]
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elementcollector1
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Incidentally, what vacuum does yours pull? The product specifications on mine state a maximum of 27.4 in. Hg (found here).
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Dr.Bob
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I don;t know what this one pulls, as it is new, so I have not used it. I use them at work, and they routinely pull down to something in that range,
but giving a maximum of 27.4 seems overly precise, since the vacuum will depend on water pressure, flow, and temp, as well as the tubing used. I
almost never use a water aspirator for anything that requires any precision, as they cannot provide a steady vacuum. I use them for filtering and
evacuating larger flasks to purge with N2, but for anything critical, even the rotovap, I use a diaphragm pump or rotary pump, as they provide a
steady rate, those can get down to 15-30 mtorr or so for rotary, the diapharm one gets in the 100 mtorr range, but the gauge is not very accurate.
Few vacuum pump gauges are very good, other than very nice ones. I have tested many against each other, and rarely get similar readings that are
within the specs given in the manual. As soon as they are used once, they start getting dirty, corroded, and less accurate. But they work for most
purposes, and most are precise enough for the job.
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