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Thread: Vacuum pumps needed

  1. #1
    Join Date
    Jun 2008
    GTA Ontario Canada

    Vacuum pumps needed

    Joe Woodworker carries a variety of vacuum pumps. A few are what are called rocking piston pumps. I tried reading about these to understand them but my brain well it cooks up its own ideas of what it wants to know.

    So a pump like i have linked to above is a rocking piston type. Does anyone here have experience of these type of pumps?

    Thing i dont quiet understand is , they mention in the manufacturers catalog that this is a compressor and vacuum pump. So my question is , does this unit operate on the basis of one cyclinder acting as a vacuum pump and the other on the same revolution of the motor but on the other side as a compressor or do both cylinders operate in tandem where a dual unit like this is just for getting greater vacuum and dealing with more airflow?

    So in this event i presume the unit is then either a compressor when you use the one output and a vacuum pump if you use the opposite end output?

    Hey what can i say i am a simple guy i need simple understanding. Before i can even venture further.

    Next question...if one connects this to a tank of sorts, and draws a vacuum on said tank say for argument sake 20gallons. Then opens the valve on the 20 gallon tank am i understanding correctly that i can get a more rapid evacuation of the item say a bag that the tank is connected to in order to say pull the bag down rapidly initially by faster evacuation of the air rushing into fill the 20 gallon tank? I realize if my understanding is correct that i will not have a full vacuum in either tank or bag at that stage but if the pump was continuously running i would surely have extracted a huge initial amount from the bag or does it not work that way in real life?

    Would it be better to simply connect a shop vac to the bag for a quicker initial draw of vacuum? and then switch over to vacuum pump. I am wanting to build a setup to do both woodworking and use the pump to try out making a vacuum forming rig but from what i see in vacuum forming i need to draw a vacuum quickly across the chamber.

    Any help understanding this appreciated thanks.

    Oh and while on the topic of vacuums has anyone given thought to or tried to "hotrod" their home foodsaver vacuum unit by hooking it up to an external pump of better performance than the junk inside at present.
    Last edited by Rob Keeble; 03-20-2014 at 08:17 PM.

  2. #2
    Join Date
    Oct 2006
    ABQ NM
    Quote Originally Posted by Rob Keeble View Post
    ...So in this event i presume the unit is then either a compressor when you use the one output and a vacuum pump if you use the opposite end output?...
    Robbo buddy, you're flirting with Analysis Paralysis again.

    Any pump, whether it's pumping air, water, oil, or wet concrete, has an inlet and an outlet. There's a vacuum at the inlet and pressure at the outlet. Some pumps (like an air compressor, have big inlets and smaller, concentrated outlets. Others (like a shop vac) have concentrated inlets and large outlets. It sounds like the vacuum pump you're looking at has an equal-sized inlet and outlet. Hook up a hose to one of them, and it sucks air. Hook up a hose to the other one and it blows air.

    I'll leave the questions about tanks and faster draw-downs to someone with more experience with vacuum bags and such.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

  3. #3
    Join Date
    Dec 2006
    RETIRED(!) in Austintown, Ohio
    Vaugn's already set you straight on how pumps work, so no further lessons needed...

    As for the type of pump, I prefer rotary vane pumps, and Gast makes the best - and most readily available - ones. The rocking piston ones are supposed to be pretty good, too, but I've not used one myself.

    Whichever kind you use, they're NOISY(!). I have a so-called muffler on mine, but I still usually set it outside, and run the hose from it under the door or through a window to the bag.

    You might try Northern Tool, or Surplus Center, or the Canadian equivalents (if such exist) for a better price than JWW.
    Jim D.

  4. #4
    Join Date
    Dec 2007
    Billings Missouri near Springfield Mo
    Also try E-bay
    As far as the tank idea you are thinking right about the draw down. I went to a limo builders auction one time and they had one it was a HUGE tank with a small pump on it they said it took over half an hour to draw down the tank (must have been a 500 gal tank or bigger) but would draw a lot of vacuum fast when they went to form limo panels.
    A Turn N Time
    Components for John Smith Organs and the Hobby Organ Builder

    Frog Pond Guitars

    Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you're a mile away and you have their shoes.

  5. #5
    Join Date
    Dec 2006
    Independence, Kentucky
    I have found that vacuum pumps used for refrigeration evacuation are a lot quieter also if this is a concern for you. I have a Gast rotary vane and it is a little loud, but it sure does pull a vacuum.
    I'm supposed to respect my elders, but its getting harder and harder for me to find one now.

  6. #6
    Join Date
    May 2007
    Thomasville, GA
    Like Charles, I have a refrigeration pump - Robinair - that is a real workhorse. I bought it from a friend who had found it at a pawn shop. You can find real bargains that way.

    As to the 'a pump is also a compressor' part, it depends. The outlet air on the Robinair, and others I suspect, has a fine mist of oil - not something you want around a wood project. I keep a wad of steel wool in the outlet port to keep the oil from disbursing in the air.
    Bill Arnold
    Citizen of Texas residing in Georgia.
    NRA Life Member
    Member of Mensa
    Live every day like it's your last, but don't forget to stop and smell the roses.

  7. #7
    Join Date
    Mar 2014
    Humid Gulf Coast
    Yeah, I don't think you would want to use the output air from a Robinair type pump for anything.

    The oil that is used is called "Pump Oil", but it is not actuly oil, it is a chemical cocktail of slippery stuff.

    It fogs out into the air so much, I wouldn't use one indoors.

    As far as drawing a vuccume, they can go down to zero and hold it for a long time.

    But these types of pumps do have a serivce live, and when the vacumme isn't drawing down, you chuck the pump and get a new one.

    I also have a Robinair, and I think the manual said do not block off the output air, meaning probably do not allow it to pressurize.

    Robinair is considered a good brand in the A/C service trade.
    It's kind of fun to do the impossible

  8. #8
    Join Date
    Jun 2008
    GTA Ontario Canada
    Thanks all for your input. I still have not managed to ascertain my original concern about this rocking piston type. Its two cylinders right and oil less, so can one cylinder be used as a compressor and the other as a vacuum or are they somehow both connected so the machine as a whole is used as either or.

    The manufacturer has specs for it as a compressor or vacuum pump, obviously there is no tank so as a compressor so its not going to make a great compressor unless hooked up to a tank to buffer it. I got the spec sheet and its pretty poor on any functional description.

    I will contact Joe woodworker and ask him about these. BTW he has machines at all ranges of prices very competitive with Ebay but with a warranty and you get to support another valuable (to us all ) small business. He does not just sell goods he also supports them and adds significant value with his service so he gets my vote over the ebay crowd. Thanks for the input all. Will update when i get some input from Joe.

  9. #9
    Join Date
    Nov 2006
    Austin, Texas
    I thought I had a page on Vacuum pumps, but I couldn't find it, so consider this a first draft.

    Two common ways of creating vacuum
    1. A rotary or other vacuum pump.
    2. A venturi driven by compressed air

    Two common ways of using the vacuum source
    1. Run the source continuously
    2. Use a tank, with controls to turn the vacuum source on or off as required.

    So that leads to a 2 by 2 matrix...

    I bought a continuous duty vacuum pump that I run for the 10 hours or so that I typically have to hold a vacuum for bent wood or veneer. Noisy, Fairly low volume, so I put a T connection with ball valve to allow use of a shop vacuum to initially empty the bag. In practice I have never (that I remember) used that option. By folding up the unused part of the bag, and squeezing out air as I seal the bag, my low volume pump can draw a vacuum in well under a minute on even pretty large bags.

    I could put a tank and control on my vacuum pump so it would only have to run intermittently rather than continuously. It might pull down a bag quicker, from the tank, and might be quieter as it runs intermittently overnight and I am trying to sleep. My vacuum pump might last longer, too. But I haven't bothered, since I bought a good quality continuous duty pump.

    I do not have a giant shop air compressor, so I was afraid to get a venturi type vacuum source (even though it would have been a lot cheaper). I have since learned that it takes remarkably little compressed air to draw a significant vacuum, so I should have given this option more consideration. You probably don't want to be blowing compressed air for 10 hours, so probably want to use this approach only with a vacuum tank and controls. Note that this kills two of the 4 squares in the 2x2 matrix.

    I have confessed what I did. But I would certainly consider one of Joe Woodworker's do it yourself plans, and possibly venturi source, if I were doing it again.

    I have been warned about used vacuum pumps. They often start life in medical facilities and chem labs, and may have mystery bacteria and chemicals. I chose to buy a new pump. You decide.

    If you are using the vacuum for a nice clean vacuum bag, no big worry. The little filter that came with my pump is adequate. However, when I tried to use it for vacuum clamping, that duty was in a dusty environment, and the vacuum pump found more dust that I believed possible. The filter was too small for that duty, and plugged in no time, so the pump stopped working. As a very fine filter it was EXTREMELY hard to clean. So if you are considering vacuum clamping, be sure to incorporate a substantial easily cleaned (or disposable) filter. Or a vacuum tank that you know will accumulate sawdust, and will have to be flushed out occasionally.

    I have tried vacuum chucking on my lathe. A small bowl or whatever doesn't have a lot of area for the atmospheric pressure to hold the work in place, even if you have a perfect vacuum on the inside. In my experience it isn't worth trying to vacuum chuck a 2 or 3 inch bowl. On the other hand, a 5 inch bowl has a LOT more area, so is easily chucked. In fact, my shop vacuum holds adequately - almost as well as the vacuum pump, for gentle finishing cuts and sanding. I haven't tried a large plate or bowl, but expect it would chuck easily for finishing work.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at

  10. #10
    Join Date
    Mar 2007
    Escondido, CA
    is your goal to understanding the pump? Or is it to try and combine a vacuum and compressed air in one machine? More importantly, how do you plan to use the vacuum pump? Veneer? Chucking? Clamping? What?

    Some thoughts: Venturi pumps required constant air. We nearly burned the school shop down one night when the compressor the size of a Volkswagen overheated. It failed and the bagged project, a sleigh bed headboard, was ruined. And the compressor was fried. Sort of turned me off to venturi type vacuum pumps. Can't walk away from them and they require an insane amount of air. Literally you need a compressor that can pump air faster than the venturi uses it.

    With regard to vacuum tanks. The air in the tank has to be evacuated along with the air in the bag. If there is a leak in the system, the tank does not supply vacuum or stated otherwise, a continuing lack of air. Only the pump can do that, and though I have built a number of them with tanks, I still do not see why they help. Oh, well.

    Regarding Joe Woodworker. I have seen and used his systems. Well thought out and they work. What more could you ask?

    Ask for rocking piston vs. rotary vane. The former is more expensive to begin with and the repairs and overhauls are also pricey. They use pump oil, a special animal all on its own and they don't give away that stuff either. And you get to buy much more than you need because it is not available in small quantities. Fun, huh? The rotary vane is much less expensive and easy to repair. Also the parts are easier to find.

    Will you get vacuum and compressed air with the same unit? Effectively, no. The compressed air coming out is 'waste' air, and dirty to boot with regard to using it in another application. In a rotary vane pump it is not oil but carbon dust. Insidious stuff. More importantly, I've not seen one of these pumps that pump out a useful amount of air or at a useful pressure.

    So that is that.

    My creds here. I developed the syllabus and taught a class on vacuum systems in the wood shop (not meaning shop or dust vacuums.) back in the very early '90's.
    Last edited by Carol Reed; 03-21-2014 at 05:02 AM.

    Some say the land of milk and honey; others say the land of fruits and nuts. All together my sort of heaven.

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    Carol Reed

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