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vacuum pumps

A

ALAN THOMAS

Joined
Jan 25, 2010
Messages
22
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Location
cornwall england
Website
www.atwoodturning.com
I am looking at installing a vacuum chucking system in my workshop but don't have a compressor to run a Holdfast type of rig. I have found a couple of electric vacuum pumps on ebay that are used in air conditioning for vehicles and refrigeration. They are made by ACTEC and are marketed as having 3cfm free air displacement and an absolute vacuum to 10pa. Since I have no idea what these values mean I was wondering if anybody could tell me if these pumps are of any use to run a vacuum chuck.:confused: Any information would be appreciated.
Alan
 
Alan,

For vacuum chucking you need a pump that will deliver at least 20" of Mercury worth of vacuum. Measured in Pascals ["Pa"] you would need a pump rated at over 750,000 Pa. For comparison, it takes about 101,000 Pa. to equal 29.5" of Hg which is close to full hard vacuum at sea level on Earth.

The pumps you reference in your post are worthless for what you want to do.
 
Many of us have been quite happy with the A/C evacuation pumps that Harbor Freight sells. Yes they are oil pumps, and you would need to buy more oil (NAPA carries it). They do drip oil out of port on top. But for the price...
http://www.harborfreight.com/25-cfm-vacuum-pump-98076.html

I got a 20% off coupon in the Sunday comics and reduced the price even more

---OPPS---- Just noticed you are in the UK. While the store doesn't apply the concept does
 
Alan,
Most of us use Gast rotary-vane style pumps like the pic attached (it's from a current ebay listing - this one has a filter attached with the piping into the pump).

  • Keep checking eBay;
  • I've seen them listed on various Craigslist ads too;
  • Google: "surplus Gast vacuum pump" on the web.

You should be able to locate one in the neighborhood of $75 - $150 for a very good used one. Visit the Gast website to compare models - both past and present.

(as N7BSN commented, I didn't realize you are in England, so use whatever information from my post that you can)
 

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I built my first one from an Automotive compressor. There are plans in an early American Woodturner. I think total cost of everything was $50. Looked kind of like an Osha Nightmare but worked perfectly. In fact I saw the guy I sold it too this last week and he's still using it 5 years later.
I found a ghast pump at the flea market and purchased it for $35. It is noisier than the Oneway pump and gets hotter but has been working perfectly for the last 5 years.
I believe the article on vacuum pumps in American Woodturner goes into the detail on size, horsepower, etc of what you need to put together a working vacuum system. If your an AAW member you can look it up in the members area because you will have access to all the Journals.
 
Thomas Vacuum Pump 607CA22C

I bought a small Thomas vacuum pump off Ebay for $85.00/$12.00 shipping last year. I made a small reservoir out of 4" PVC and a couple of caps. Pulls 24+" HG and works just right for everything I've done.
 
Mark Mandell said:
Alan,

For vacuum chucking you need a pump that will deliver at least 20" of Mercury worth of vacuum. Measured in Pascals ["Pa"] you would need a pump rated at over 750,000 Pa. For comparison, it takes about 101,000 Pa. to equal 29.5" of Hg which is close to full hard vacuum at sea level on Earth.

The pumps you reference in your post are worthless for what you want to do.
Click to expand...

Mark, I believe that you may have misinterpreted the vacuum pump's spec on pressure. Alan said that the vacuum was given as absolute pressure, but your response assumed relative differential pressure.

With an open port flow of 3 CFM and blocked port vacuum (10 Pa) that is adequate for pumping down a refrigeration system, it appears that the system would work just fine for vacuum chucking. The only caveat is that if the pump has oiled vanes/piston then wood dust will gradually contaminate the oil and require more frequent maintenance. My preference is a dry rotary vane pump. It can't achieve the hard vacuum that a piston or oiled vane pump can, but it is great for vacuum chucking.

Mean sea level pressure for standard day conditions is approximately 29.92 in-Hg. However, if we were using a vacuum pump to evacuate a refrigeration system before charging it, a differential pressure reading is mostly useless if we wanted to know whether the pump was capable of achieving a hard vacuum unless we also knew precisely the barometric pressure. By measuring absolute pressure, we can do away with the error introduced by making a separate measurement of atmospheric pressure.
 
Thanks a lot for your help guys. It is much appreciated. As I live in the UK the choice for hardware is a little limited and after thinking it over again I think I will go back to my original shopvac solution.The cost factor always plays a part in this type of decision and the vac pump I outlined is 3x the price of a shop vac ($ 170 v $ 65 ). I have been using a shop vac for some time but it died a couple of days ago and I wanted to explore other systems. If I decide to upgrade my system at least now I have a little more information to work with.
 
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are the different between a vacuum pump and a air compressor in the check valve that permit flow only in one direction ? can the valve be reverse to change a air compressor into a vacuum pump ?
can a small gasoline engine be modified to serve as a vacuum pump
 
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ALAN THOMAS said:
Thanks a lot for your help guys. It is much appreciated. As I live in the UK the choice for hardware is a little limited and after thinking it over again I think I will go back to my original shopvac solution.The cost factor always plays a part in this type of decision and the vac pump I outlined is 3x the price of a shop vac ($ 170 v $ 65 ). I have been using a shop vac for some time but it died a couple of days ago and I wanted to explore other systems. If I decide to upgrade my system at least now I have a little more information to work with.
Click to expand...

Alan,

IIRC the shop-vac-cum-vacuum-pump option was started by the Aussies. If you're going back to that, you'll do well to invest in a vac the uses a secondary airflow to cool the motor. Most vacs use the "cleaned" airflow to cool the motor by routing it through the windings. When you use one of those machines as a vacuum source, you cut off the cooling air and the motor burns out in a relatively short time. In the long term, investing in a real vacuum pump will be cheaper than replacing your shop-vacs.
 
vac pump v shopvac

Hi guys
Just thought I would update you on the vac pump v shop vac saga. I have discussed the pro's and cons with a couple of guys that run shop vacs and they all say that a shopvac is fine for an occasional and short period but the motors overheat fairly quickly and burn out if used on a regular basis. As I intend to use this system often I am going to buy a proper vac pump. I have found a supplier of pumps very much like the ones sold by Harbor Freight and they are not too expensive. My only problem now is how to sneak my new shiny toy past SWMBO ;)
Thanks again for the help
Alan
 
ALAN THOMAS said:
... My only problem now is how to sneak my new shiny toy past SWMBO ;)
Thanks again for the help
Alan
Click to expand...

See if your supplier has an old, filthy, non-working pump that's going to be scrapped. Give him a couple pounds for it and sneak it into the house. Then present it to your wife as broken and you had to replace it with the shiny new one. Reveal this after you already have the new one in hand.
 
Alan I used a shop vac for a while after buying my Nova Comet lathe. The adaptor that Nova sells for the shop vac has a simple hole drilled in the side to let some air leak out. This was designed to keep the Vac from overheating so it said in the manual. I didn't use mine for long periods and didn't have any trouble with overheating.
 
John Lawson said:
See if your supplier has an old, filthy, non-working pump that's going to be scrapped. Give him a couple pounds for it and sneak it into the house. Then present it to your wife as broken and you had to replace it with the shiny new one. Reveal this after you already have the new one in hand.
Click to expand...

Devious! Very devious!
[the man's a genius, I tells youz. A genius]:D:D
 
shop vac v vac pump

I have come to an arrangement with SWMBO. I fix her houshold machines within 30 days ( I didn't say that I would give any guarantees ;) ) and she doesn't complain about my new toys :D
My original shopvac system utilised the plastic handle of the machine and this had a venting slide which could be opened to allow air into the hose. One of the main problems that caused the overheating was that the motor ran in bushings not bearings so that once the bushings started to wear the heat built up very quickly and even venting through the slide it overheated within a minute or so and took a long time to cool down.
I am expecting delivery of my new vac pump tomorrow and I will let you know how it works out.
 
Rebuilt pumps

Alan, you might try to contact Johnny Tolly in Austin, TX. He has been rebuilding Gast style pumps for resale. I do not know if he is still doing it but several people I know of have gone that direction and are extremely happy. He is an aaw member so you should be able to contact him.
 
Bill Pottorf said:
Alan, you might try to contact Johnny Tolly in Austin, TX. He has been rebuilding Gast style pumps for resale. I do not know if he is still doing it but several people I know of have gone that direction and are extremely happy. He is an aaw member so you should be able to contact him.
Click to expand...

Bill, I think that the expense of shipping to the UK would make that a not very good option. Years ago when I bought a used pump on eBay, the UPS shipping charge for shipping from North Dakota to Texas was in the neighborhood of $40. I hate to think how much it might cost to travel across the pond.

In addition to that, there might be a problem with the operating voltage and frequency for the motor. I do not know about the UK, but much of Europe uses 50 Hz power. Gast and other manufacturers may have models that use different motors for use in European countries.
 
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gast vac pumps in the UK

Bill, thanks for the suggestion on the source for a gast pump but postage to the UK makes them too expensive and the electrics are different. There is a Gast supplier in the UK but they don't sell reconditioned or used units of the type I want and the cost of a suitable new pump works out at around $570. The pump I have gone for is the one I mentioned in my original post and costs about $168.
 
Alan, I did not realize you were in the UK. I would not have suggested this. Sorry!
 
I have a very primitive looking pump. It looks like a compressor of very old fridges. When I upgraded my lathe two months ago the pump came with it. The previous owner was a technician to repair car air conditioning system and he used it to remove freon gas from air conditioners. I was told I should be able to get one in future from auto parts suppliers. It doesn't look expensive.
If someone interested in it, I would try to load a picture of it tomorrow,
since it is almost 12 pm now.
 
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