HollowMan
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Which vacuum gauge for distilling
Hi community,
right now I´m standing for a few questions.
I want to buy a new vac gauge like the MKS TRANSDUCER 901P-11040 (http://www.ebay.de/itm/251866499556) maybe combined wit a PDR900 controller. I have no experience with this kind of vac gauge I just used a testo
552 vac controller before, which was everything else as accurate. The main question is, can I just make measurements about the pump itself (what
ultimate vac is available) or can I use it for distillation, too?
I read most of the parts of the manual, which told me, that if the sensor (transducer) is contaminated by a liquid (such as pump oil) it can´t be
cleaned and might be sent in for repairing. I want to use it for distillations in the range of around 8mbar (for example aetheric oils). I have no
possibility to use a cooling trap in front of the transducer so I´m not sure how much contamination can be expected? The reason why I want to just
such an exactly operation system is because I´m owner of an high vac pump , too and I want to check up their ultimate pressure time to time (to be
prepared for oil change).
So do you think it´s an good investment for my usual operations without having to replace the transducer after short time usage?
Your advices would be really appreciated.
Thanks in advance 
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Magpie
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I have one of those expensive electronic piranyi vacuum gages (Pilot something). I wouldn't think of using it for distillations because of sensor
contamination. I use a Bennert manometer for my vacuum distillations.
The single most important condition for a successful synthesis is good mixing - Nicodem
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HollowMan
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For what are you using the expensive ones if I may ask? This sounds plausible to me, but usually the contamination isn´t much, if you use good cooled
cooler i think. And I would put a three way chart in front of the pump wherefrom one way leads to the transducer. So it´s not directly placed into
the distilling stream. I really try to avoid the Bennert one. Did you experience on your own contamination problems by using this kind of transducer?
This one is really cheap just for 45$ on ebay right now.
regards
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Magpie
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I bought the Bennert first on eBay, without mercury. I filled it myself then wanted to check its accuracy as it must be completely evacuated before
filling. So I bought the Inficon Pilot Plus to check on the accuracy of the Bennert.
Somehow I contaminated my Pilot's sensor - vacuum pump oil I believe, probably due to operator error. I replaced the filter on the Pilot with a
spare.
$45 is not bad. I think mine was ~$100. If you are sure you are isolated and don't screw up in using it you will likely be OK. Of course one can
contaminate a Bennert also.
The single most important condition for a successful synthesis is good mixing - Nicodem
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HollowMan
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For me it´s first time use with kind of this stuff soI´m not sure if i´ll screw up. But it´s connected to a diaphragm pump during distillation.
Its just placed on the high vac oil pump for checking ultimate vacuum. Usually there should be no contamination. I´m just worried about distillation
vapors if the may have contact to the sensor. I never had the chance to try it. I also don´t now what contamination should mean in this case: is it
some drops or some mg of distilled vapors? Does it stay on the transducers surface and going to be more and one time the sensor stops working? Usually
this kind if transducer kosts about 300$ if new.
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Magpie
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If I wanted to be super careful I would place an isolation valve right at the gage before the tee into the system. Keep that valve closed until the
system is at a full and steady vacuum, then open it very slowly. Close that valve again before bringing the system up to atmospheric pressure.
Remove the gage with the valve as a unit. Then slowly open the valve to the ambient atmosphere.
Or something equivalent to this.
The single most important condition for a successful synthesis is good mixing - Nicodem
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aga
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Is there a dirt-cheap vacuum sensor out there that you've tried ?
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Magpie
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I used to use a cheap vacuum gage from the hardware store, ie, the one shown below. 10 years ago it was like $10. The units are inches of mercury.
It's Ashcroft brand.
If you have enough mercury you could make your own gage with ~5 feet of 6mm glass tubing.
The single most important condition for a successful synthesis is good mixing - Nicodem
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HollowMan
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AlrightI´ll give it a try. I thought about a cooing trap by using CO2 in aceton or pure. But there is my next question: are there some pressure boxes
available, where it´s possible to store the solid CO2 without loosing it? Must refrigerators just reach about -22°C thats a bit to less
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Lambda-Eyde
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Quote: Originally posted by HollowMan  | | But there is my next question: are there some pressure boxes available, where it´s possible to store the solid CO2 without loosing it?
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No:
This just in: 95,5 % of the world population lives outside the USA
You should really listen to ABBAPlease drop by our IRC channel: #sciencemadness @ irc.efnet.org
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Mush
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Are these Digital Vacuum Gauges suitable for laboratory usage?
Details about CPS Products VG200 Digital Vacrometer Vacuum Gauge
US $156.00
https://www.youtube.com/watch?v=T7J1YAuWzKQ
Yellow Jacket 69047 eVac
US $157.89
BluVac Digital Vacuum Gauge
US $211.21
0.1 Micron Resolution!!!
https://www.youtube.com/watch?v=cI6pSBaskjc
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Magpie
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Very informative videos. I didn't look up the specs on the Yellow Jacket which I assume is of equal capability.
For vacuum distilling the pressure range, in my experience, has been in the range of 1-100 mmHg. This is the same as saying 1000-100,000 microns.
Since those gauges read down in the single digit micron range they are overkill. But, to answer your question: yes, they would work well assuming
they read in the 1000-100,000 micron range as well.
They are expensive and a mercury manometer would be much cheaper, but would only read to the nearest 1 mmHg. But you don't need more than that for a
typical vacuum distillation.
http://www.ebay.com/itm/Dwyer-Flex-Tube-Series-1221-U-Tube-M...
The videos don't say how susceptible they are to contamination but his emphasis on keeping the caps on until use is a big clue.
If your technique (skill) in using one is not good and you ruin it by contamination - well - you may be out $150 - an expensive lesson. It's likely
you can clean it up with a little alcohol, however.
It may be hard to find mercury manometers anymore - check eBay. What we need is a good Bourdon gauge reading in the 1-100 mmHg range .
[Edited on 3-5-2015 by Magpie]
[Edited on 3-5-2015 by Magpie]
[Edited on 4-5-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Sulaiman
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Although cheap this seems to work http://www.ebay.co.uk/itm/281397111589?_trksid=p2057872.m274...
but my vacuum pump is only -80 kpa (c160mm Hg absolute) http://www.ebay.co.uk/itm/311057103383?_trksid=p2057872.m274...
it would however be useless at differentiating between 1 and 2 mm Hg
even 10 and 20 mm would be only a small indication.
this pump reduces the boiling point of water to about 63C
I bought the gauge just to monitor the partial vacuum
as the main purpose is just to vent stuff like NOx out of my shed/lab
off to the lab now to confirm the 63C which may be incorrect.
..............................................................................................
EDIT: just tested the pump, tap water boils at 63C.
which an online calculator tells me is equivalent to c165mm Hg absolute
not too bad considering it was pumping water vapour.
if anyone considers a similar pump;
. 12V dc at c1.5A continuous BUT c3A 'surge' to start if vacuum present,
. I silicone greased the crank bearing because it got hot quickly as supplied (dry).
. not too noisy
[Edited on 4-5-2015 by Sulaiman]
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Mush
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| Quote: |
They are expensive and a mercury manometer would be much cheaper, but would only read to the nearest 1 mmHg. But you don't need more than that for a
typical vacuum distillation. |
I like those U tube manometers, only issue is getting mercury to fill them up. Hard to came by these days.
| Quote: |
It may be hard to find mercury manometers anymore - check eBay. What we need is a good Bourdon gauge reading in the 1-100 mmHg range .
|
I spent 2 day on ebay searching for accurate (1-100 mmhg) vacuum gauges, these ones just simply don't exist.
For general vacuum distillation this one is alright:
http://www.ebay.com/itm/76cmHg-30inHg-1-4PT-50Vacuum-Pressure-Gauge-50MM-Better-US12-/171557965495?pt=LH_DefaultDomain_0&hash=item27f1a6ceb7
unites are in inHg (30) and mmHg (76), resolution is 20 mmHg bottom range.
| Quote: |
it would however be useless at differentiating between 1 and 2 mm Hg even 10 and 20 mm would be only a small indication. |
Exactly. I am affraid I will have to invest in an expensive vacuum gauge if I want to measure between 1-10 torr.
Ohh, and what about digital differential pressure gauges, like this one?
http://www.aliexpress.com/item/Pressure-Gauge-psi-XINTEST-HT-1895-Portable-LCD-Digital-Manometer/1995954730.html
I'm wondering if it's accurate close to 0 atm.
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gatosgr
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you can make your own gauge http://www.belljar.net/tcgauge.htm
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Sulaiman
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Mush, the cheap vacuum gauge that you pointed to
appears to be similar to mine except a differently printed face.
(they all come from the same place
The gauge displays from atmospheric down to (atmospheric - 760 mm Hg)
'zero' is atmospheric pressure which is variable
(925.6 mbar (26Jan1884) to 1053.6 mbar (31Jan1902) which is quite a wide range for a U.K. reference)
In the test that I did this morning the water boiled at 63C (+/- <1C)
(thermometer bulb in liquid or steam)
which is 22 kpa (+/- 1 kpa) according to an online calculator
(-78 kpa relative to atmospheric)
the gauge read -0.0750 Mpa = -75 kpa
(a nearby Meteorological office reading 1002 to 1003 hPa during the time of the experiment, 100.25 kpa average)
there is no way to reconcile those numbers, the simplest conclusion is
the vacuum gauge is unreliable for low absolute pressures.
EDIT: for £3.76 incl. p&p etc. it would be unfair to expect more of the (partial) vacuum gauge !
and it suits the pump that I use with it with......
It would be nice to know where 0 pa absolute pressure is on my gauge though
Could any one suggest a simple/cheap way to achieve a temporary near absolute vacuum for reference, e.g. < 1 mm Hg?
(due to cost and/or availability, no liquid air/nitrogen/helium, no dry ice)
[Edited on 4-5-2015 by Sulaiman]
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gatosgr
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When I was going to build an accelerator I was going to build this but I gave up on this project.
http://www.cientificosaficionados.com/tbo/difusion/difusora1...
In america you can get a used one for 50$
[Edited on 4-5-2015 by gatosgr]
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Mush
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Great stuff!
I doubt one can get a diffusion vacuum pump for 50 dollars anywhere. The guy says it costs 1500 euros (band new), used available for 350 euros in
Europe.
Thanx Sulaiman!
So, the error is about +-3 kPa. 
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gatosgr
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Just search on ebay they sell used ones http://www.ebay.com/itm/Diffusion-Pump-14-TALL-5-1-2-FLANGE-... but if you live in europe like me then you better make it yourself. Of-course you
need to buy the oil separately.
[Edited on 5-5-2015 by gatosgr]
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