Sciencemadness Discussion Board

Manometer, vacuum meter.

User - 21-12-2010 at 14:26

Good evening.

I am rather lost :)



A while ago I bought a pre owned vacuum pump.
There is no meter or what so ever on the pump itself.
So obviously I need to buy one.


There are thousands of meters for sale ranging from dirt cheap to really expensive, precise , glycerin filled, digital, etc etc.
What are the criteria for buying one ?
I have barely any experience with vacuum operations and i'm planned to practise some simple destillations.
My needs will probably evolve over time and it would be nice to keep this in mind.


How much is reasonable to spent ?
Anything I should be aware of ?




Thanks in advance :)
Btw I live in the Netherlands.

IrC - 21-12-2010 at 15:07

Not easy to answer until we know how much of a vacuum can your pump do. If typical (greater than a few hundred microns - meaning not really high vacuum) then this type is easy to implement and works well, at a low price.

http://cgi.ebay.com/Yellow-Jacket-49138-3-1-8-Low-Side-Manif...

If high vacuum then ion gauges come to mind.

http://cgi.ebay.com/Duniway-I-100-K-Ion-Vacuum-Tube-Gauge-/3...

also a thermocouple type:

http://cgi.ebay.com/Varian-Vacuum-Thermocouple-Gauge-Sensor-...

A few more low cost but good:

http://cgi.ebay.com/Gauge-2-Vacuum-Gauge-0-30-HG-0-1-BAR-1-4...

http://cgi.ebay.com/VACUUM-GAUGE-1-4-NPT-BOTTOM-CONNECTOR-0-...

http://cgi.ebay.com/U-Tube-DynaMeter-Manometer-Vacuum-Gauge-...

http://cgi.ebay.com/Manometer-old-style-Meriam-10AA25FF-10-u...

U Tube Dyna Meter Manometer Vacuum Gauge above or older Hg type if this is the way you wish to go. I have a few Hg types as well as the Hg for them but I prefer not to muck around with them. If I wanted a precise high vacuum type then I would go ion.

Need more info about what level of vacuum (or lack thereof) you are going to be dealing with.

Of course most eBay links will mail to you no problem. Also likely all these links will be dead in a few days so search again when you are ready. Quite honestly I find eBay to be a damn easy way to find much of the madsci items we know and love.

Forgot to mention but if distillation work is your main focus you do not need ion types or Hg, etc., one of the cheap 0-30" I linked here is just fine. A side note is get a large one (5 or 6 inch diameter) for better discernment of small changes.




[Edited on 12-21-2010 by IrC]

chemrox - 21-12-2010 at 19:16

There's quite a difference of ranges among these. I would run up a distillation and check boiling point lowering. Nomographs for determining vacuum from boiling points ate available on-line as well as the backs of many lab manuals. I think the organic chemistry survival manual has one but I'm not sure. I gave my copy to my daughter.

IrC - 21-12-2010 at 19:50

Quote: Originally posted by chemrox  
There's quite a difference of ranges among these. I would run up a distillation and check boiling point lowering. Nomographs for determining vacuum from boiling points ate available on-line as well as the backs of many lab manuals. I think the organic chemistry survival manual has one but I'm not sure. I gave my copy to my daughter.


I gave a wide selection to cover all bases not knowing where his pump will go, or at least where he needs to run it. Looking at the pdf I have to say it appears all he needs is one like the yellow jacket link I posted, since 8" Hg to 29" Hg is the entire range needed. Assuming whatever he is distilling is similar to water for BP VS pressure. Since he needs a T for the gauge and another for a bleeder using a manifold in place of 2 T's is a good idea. One outlet is the gauge and the other goes to a bleeder valve. The needle type such as is used for swamp cooler water will do. When the pump is powered it will run at whatever flow it can do, no control of vacuum exists unless you open a bleeder valve to let air in to achieve a steady vacuum of the desired pressure. Put the bleeder closer to the pump than the gauge, which should be closest to the experiment. If the pump is a powerful one you may need to play with inlet to manifold tubing size to restrict flow (or add a metering jet) to allow the bleeder to give you the full range needed. Unless the pump is run by a DC motor (never seen one other than small automotive types) meaning if it has an AC motor never try to control power to the motor.

Attachment: WaterBoilingPointsatVariousPressures.pdf (9kB)
This file has been downloaded 626 times





[Edited on 12-22-2010 by IrC]

User - 21-12-2010 at 23:54

Tanks for the reply's :)

I am not at home right now, and will not be for a couple of days , so I cannot do any testing right now.
Could not remember the name yesterday otherwise i would have posted this earlier.


It is a single stage rotary pump.
An edwards speedivac 2.
According to multiple sources its max vac. is 1.3x10-1 mbar, with a flow rate of 2.7 cubic meter p/h.


It also is old and i might need to take the thing apart and clean it for better performance..

IrC - 22-12-2010 at 03:03

Cleaned up with new oil is good as well a clean inlet filter to protect the pump. I would want another port on the manifold to add an ion gauge along with the big meter Yellow Jacket gauge. Easy to see where you are at ballpark for general use and you have accuracy in the high vacuum range below a hundred microns. Manifolds are around but you can also drill and tap a large diameter piece of brass rod.

Contrabasso - 26-12-2010 at 12:21

Reactions and thermionics in vacuum will need a much better vacuum than simple reduced pressure distillations. Also any attempt to pull vapours through the pump will seriously contaminate the oil and cause the ultimate vacuum to be impaired.

I use a fridge pump for vac work! It's cheap enough to be disposable and will achieve a fair depression