Sciencemadness Discussion Board

McLeod Manometer Hg issues

organicchemist25 - 1-1-2018 at 06:25

I bought a McLeod manometer a year or so ago and finally got around to getting the tripe distilled Hg to put into it. I bought the gauge from Ace glass. Upon filling I could not get it to read both side of the gauges. The one for normal pressure would just keep going all the way up and refilling into the bulb. The bottom bulb on the left would never quite fill up and begin to raise in the tiny capillary at all, but the other side would overflow. Never used one before. I did watch a few videos and how they use it seems rather simple.

The manual from ace does not help at all. It does state "about 20 ml of Hg is required". I have searched and come up with nothing on how to fill it and get it up and working properly.

I messed with that thing for over an hour in the hood. I started with the 20 mL and then gradually tried a ml less every time (because it seemed over-filled) until about 13ml. I just don't get it.

So, if anyone has any knowledge on getting it running and techniques etc I would really appreciate it!

Happy New Year 2018!!!

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organicchemist25 - 1-1-2018 at 06:27

Oh, and, Im using a ChemGlass 10 torr PTFE pump. I feel that should be adequate for the gauge to work.

organicchemist25 - 1-1-2018 at 06:31

Lastly, the only thing I can think may be an issue is temperature.

The lab is unattached to my house and out in the yard. It is insulated well and has new electrical and plumbing, but when I was messing with this it was about 4 degrees Celsius (40 F), but I did turn heat on and the mercury was flowing like normal. I would imagine room temp being optimal, but figured the gauge would still operate.

Thanks

[Edited on 1-1-2018 by organicchemist25]

unionised - 1-1-2018 at 07:34

You have a gauge that reads between 1 and 0.001 mmHg, and a pump that will produce a "vacuum" of 10 mmHg.
Why did you "feel that should be adequate for the gauge to work. "?

yobbo II - 1-1-2018 at 10:39

Why do you need tripple distilled? What is so difficult and important to remove from the mercury?

wg48 - 1-1-2018 at 12:08

Quote: Originally posted by unionised  
You have a gauge that reads between 1 and 0.001 mmHg, and a pump that will produce a "vacuum" of 10 mmHg.
Why did you "feel that should be adequate for the gauge to work. "?


Yes unionised is correct. The gauge can not be used at too higher pressure because when rotated into the reading position the mercury will not fill the bulb on the bottom of the left hand glass tube and may overflow the middle tube and into the connection tube at the back particularly so if you put too much mercury in it.

A part from ensuring it was clean and dry prior to filling it with the correct quality and quantity of mercury I know of nothing else required for set up.

The bottom line is the gauge is not suitable for measuring the vacuum of a piston type flapper valve pump that only achieves on a good day ten times the maximum reading of the gauge.

A simple absolute pressure U tube mercury manometer is all you need or a machanical gauge.

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organicchemist25 - 1-1-2018 at 13:25

Quote: Originally posted by yobbo II  
Why do you need tripple distilled? What is so difficult and important to remove from the mercury?


I’m not real sure, but it said triple distilled is to be used...I thought it was overkill.

organicchemist25 - 1-1-2018 at 13:42

I bought this pump about a month ago and put the spec oil in it and I know it goes way below one torr/mmHg and wanted to try my 10 torr pump first. I just thought the chemglass would start to give me an idea on the gauge and functionality before I really pulled down on it.

I just want a solid gauge to know what pressure I’m distilling at.

If anyone knows a really good one I’ll buy that too. It’s about the last thing I’m dicking around with in my setup.

I just want solid readings. I don’t really care about cost.

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weilawei - 1-1-2018 at 15:48

I bought a Televac Vacuguard with a 2A sensor on eBay for $100 and a mechanical gage (a Yellow Jacket 69044) off Amazon for $38. Between the two of them, they cover 760 Torr down to 1 mTorr quite nicely. The Vacuguard runs on a single D cell battery, and it will read from 20 Torr down to 1 mTorr. The mechanical gage covers 760 Torr down to about 10 Torr with decent accuracy.

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That photo shows it at 4.6 Torr, although the pump will run down to 13 mTorr on an average day. I was having tubing issues, so I wasn't letting it pull quite it's full vacuum.

[Edited on 1-1-2018 by weilawei]

organicchemist25 - 2-1-2018 at 08:48

Quote: Originally posted by weilawei  
I bought a Televac Vacuguard with a 2A sensor on eBay for $100 and a mechanical gage (a Yellow Jacket 69044) off Amazon for $38. Between the two of them, they cover 760 Torr down to 1 mTorr quite nicely. The Vacuguard runs on a single D cell battery, and it will read from 20 Torr down to 1 mTorr. The mechanical gage covers 760 Torr down to about 10 Torr with decent accuracy.

Very nice! Does the 2A need to be calibrated? I’m ready to order one. Thank you!



That photo shows it at 4.6 Torr, although the pump will run down to 13 mTorr on an average day. I was having tubing issues, so I wasn't letting it pull quite it's full vacuum.

[Edited on 1-1-2018 by weilawei]

weilawei - 2-1-2018 at 10:03

The manufacturer (Televac made the 2A sensor in this case.) suggests calibration with a vacuum standard, however I used the boiling point of distilled water to calibrate mine and it was spot-on as received. There's no adjustment mechanism on the gage or controller, so you'd need to make your own adjustments on paper.

[Edited on 2-1-2018 by weilawei]