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IndustryArena Forum > Manufacturing Processes > Milling > Seek advice on small vacuum pump.
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  1. #1
    Join Date
    Jul 2012
    Posts
    89

    Seek advice on small vacuum pump.

    Hi all,

    I've recently bought a small ½ HP rotary vane type vacuum pump which by specification should be capable of 4.5 CFM of air flow and generating an ultimate vacuum of 0.3 Pascal.

    I use this pump for a small vacuum table and in some cases it works well - BUT if there's a small leakage between the vacuum table and the workpiece the vacuum pump's exhaust filter gets completely soaked in oil in about 10-20 minutes. This does not happen when the vacuum table to workpiece seal is complete/perfect.

    However, even if the air leak is so small that it doesn't cause the workpiece to break loose, nor causes a high air flow, the exhaust filter still gets soaked in these 10-20 minutes. And actually to the extent that the oil starts leaking out of the pump and, well, goes elsewhere ... Not really great ...

    Which brings me to my question: Is this normal or could it be that the pump's oil filter design is flawed?

    And second: Can I within a reasonable budget get the same vacuum and air flow from an oil free vacuum pump (and if so which type/model would be suitable)?

    I hope some of you have good experience with such pumps & would appreciate your input ...

    Cheers & thanks

    Jesper

  2. #2
    Join Date
    Dec 2013
    Posts
    5717

    Re: Seek advice on small vacuum pump.

    I have a similar vacuum pump and exactly the same thing happens. Enough so that it can fill the shop with an oil fog in a few minutes. I just put a long line on it and set it outside the shop. I don't use it very much so it has not really been a problem.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
    Join Date
    Jul 2018
    Posts
    6254

    Re: Seek advice on small vacuum pump.

    Hi Evalon - This is normal for that type of pump. What is happening is the moisture in the air is boiling and the steam (created in the pump) is evaporating the oil causing the fog. If you have a sealed system no air gets in so no steam, so no fog. More expensive pumps have an oil separator system so the fog is condensed and returned to the pump.

    https://www.buschvacuum.com/au/en/pr...rc-0010-0016-c

    The pump you have is designed for pulling down air conditioner systems and they require the system to have no leaks so the fogging does not occur. I don't think a dry system will get the same pressure but for a hold down you don't need 0.3 Pa. There are many cheap chinese vac pumps around with seperators, if you have a good compressor you can look at venturis as well. They are commonly use for vac hold downs.

    Air Venturi Vacuum Generator Pumps Create A Vacuum Using Compressed Air For Vacuum Workholding, Fixturing, Clamping, Solid or Liquid Materials Transfer

    Cheers Peter

  4. #4
    Join Date
    Nov 2012
    Posts
    1267

    Re: Seek advice on small vacuum pump.

    As Peter said, some "real" vacuum pumps (such as Busch) have oil separators. There are also oil-less rotary vane pumps (such as Becker VTLF series), they are commonly used with woodworking CNC machines where you don't really want any oil spraying around.

    The Chinese also make Becker-like dry pumps that work amazingly well for the price.

  5. #5
    Join Date
    Jul 2012
    Posts
    89

    Re: Seek advice on small vacuum pump.

    Hi all,

    & thanks so much for your feedbacks ... Reading your replies makes me wonder if I then bought the wrong pump - and then again, no, I probably didn't because the budget is tight and besides using it for the vacuum table I will also be using it for a vacuum annealing chamber soon to come. And here the low vacuum will be needed.

    However, it is in no way feasible to have oil leaking out when using the vacuum table ... So finding a suitable oil separator system could be a way to go - or maybe I can make one myself. Looking at ebay they appear to basically consist of filter and encapsulation for the filter.

    Also ensuring a completely leak-free vacuum table hold down could be a way to do it - but that may not always be straightforward with small parts. Hmmmm ... I actually live in Denmark, and Busch is Danish, and I even have had contact with them before - so maybe that would be a way to go ... will just consider ...

    Anyway, thanks for your clarifying replies!

    Cheers,

    Jesper

  6. #6
    Join Date
    Sep 2019
    Posts
    197

    Re: Seek advice on small vacuum pump.

    Hi, i am glad you posted this thread. I also bought a hvac vacuum pump for my vacuum table. With mine i plan to use a pressure "pot" but i have no idea if it will work.

    Will be keeping an eye on this thread! Thanks
    Erick

  7. #7
    Join Date
    Jul 2018
    Posts
    6254

    Re: Seek advice on small vacuum pump.

    Hi Ericks - Why use a pressure pot? A pot is put in line before the pump if you are pumping something that may get into the pump (so the pot catches it before it gets to the pump) . eg resin or liquid. Pumps don't like ingesting epoxy for instance if you are degassing it. Some people use a receiver in the view its like compressed air in that you are "saving" or creating more vacuum capacity. This is a false idea. You can't save vacuum like you can compressed air. The least plumbing used is the best plan, this reduces the load on the pump and it can work more efficiently. Cheers Peter

  8. #8
    Join Date
    Sep 2019
    Posts
    197

    Re: Seek advice on small vacuum pump.

    Yes the pot is there in case junk is sucked in from milling....

  9. #9
    Join Date
    Jul 2018
    Posts
    6254

    Re: Seek advice on small vacuum pump.

    Hi Ericks- excellent strategy you will need a filter as well. Some cloth or car air filter. The sawdust does get through my bucket size pot into the pump oil, speaking of which its due for an oil change... Peter

  10. #10
    Join Date
    Sep 2019
    Posts
    197

    Re: Seek advice on small vacuum pump.

    For sure a filter was planned. I am going to make an automated system. Microcontroller based with vacuum sensors etc

  11. #11
    Join Date
    Nov 2013
    Posts
    4282

    Re: Seek advice on small vacuum pump.

    Hi,

    This is a false idea. You can't save vacuum like you can compressed air. The least plumbing used is the best plan, this reduces the load on the pump and it can work more efficiently
    I use a vacuum to bag epoxy/glass on foam. I require only 1-2 psi vacuum or the foam gets crushed. To do this I have a vacuum ballast, a largish tank. This means
    that the pump cycles every 15-20 minutes for 20-30 seconds at a time whereas without a ballast tank it cycles every minute or so but for just a few second each time.
    This gives the pump motor a hard time....ergo I use a ballast tank.

    Craig

  12. #12
    Join Date
    Nov 2012
    Posts
    1267

    Re: Seek advice on small vacuum pump.

    Quote Originally Posted by peteeng View Post
    Some people use a receiver in the view its like compressed air in that you are "saving" or creating more vacuum capacity. This is a false idea. You can't save vacuum like you can compressed air.
    Actually yes, you can. Vacuum receivers are used on machines like membrane presses where you need to quickly evacuate some fixed amount of air. It allows you to use a much smaller vacuum pump.

  13. #13
    Join Date
    Jul 2012
    Posts
    89

    Re: Seek advice on small vacuum pump.

    Hi all,

    Just read and thought about the discussion you have on whether or not a a tank makes a difference in terms of "saving vacuum". I think it may be related to the gas equation P*V=n*R*T ... Although applying to a closed system I think it may help explain this:

    If one assumes that the temperature is constant (and R is a constant) then the equation may be simplified to P*V ~ n. In this case if V is small the pressure will go up a lot if the number of moles changes just a bit (n= number of moles in the gas) like it could if there were a sudden leak in the vacuum table to material contact, whereas conversely, if V is large the same number of mole change will only lead to a limited change in P. Thus the vacuum is almost maintained.

    Additionally, I think that in some cases it may also be relevant to consider the pressure variations coming from the pump if the "filtering" volume (i.e. just a small diameter hose) is insufficient.

    In my case I use a small one liter gas bottle I salvaged from our local recycling centre. Even this limited volume corresponds to about 80 meters (to my memory) of the inner volume of the hose I use (4*6mm) but it doesn't have the pressure/vacuum drop that the hose would have had. Also, I have placed this small bottle about 30 cms hose length from the vacuum table so that should there be a sudden leak the sudden flow in the hose will not cause too much of a vacuum drop. It works fine (apart from the vacuum pump oil leak etc. ... )

    Cheers,

    Jesper

  14. #14
    Join Date
    Nov 2013
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    4282

    Re: Seek advice on small vacuum pump.

    Hi,

    It works fine (apart from the vacuum pump oil leak etc. ... )
    I'm sorry you are not going to be able to avoid it, it is how rotary vane vacuum pumps work. If there is any significant flow through the pump it
    WILL generate an oil mist. Single stage pumps are quite useful for resin degassing, resin infusion, vacuum hold downs etc.
    Two stage pumps are really required for refrigeration work, vacuum drying or as a backing pump to diffusion or turbo pumps.
    In all cases if there is a vacuum leak which allows a flow through the pump you get oil mist.

    The choices are:
    1) fix the leak
    2) use an oil free pump like a scroll pump or piston pump.

    Craig

  15. #15
    Join Date
    Mar 2003
    Posts
    35538

    Re: Seek advice on small vacuum pump.

    There are oil-less rotary vane pumps.
    I have a small Gast.
    Becker makes quite a few.
    https://www.beckerpumpsales.com/beck...cuum-pumps.php
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  16. #16
    Join Date
    Jul 2012
    Posts
    89

    Re: Seek advice on small vacuum pump.

    Hi Craig & Gerry,

    Thanks for your replies ... As it is it is not acceptable with the oil leak - and given the small sizes I mill on my CNC it could be a challenge to seal all air leaks. So I reckon that in due time I will have to either replace the pump or find a way to separate the oil mist from the air that does not clog up the filter nor leads to leaking oil. Right now I am considering increasing the air flow path through the filter (a "longer" filter), and maybe another geometry, so that while the exhaust air is efficiently filtered the filter is not clogged up. "Pondering in the background" - other projects as well ... ;-) ...

    Cheers,

    Jesper

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