vacuum pump for experiments

Chuck Sherwood wrote:


Here are a few things to look for. Some of these you can only check if you can see the pump in person, but that's always a good idea if it's nearby.
* Check out the general physical condition: does the pump appear to have been looked after well or is it knocked around and covered with grime and rust?
* Ask the seller what is has been used for. If it has been used in industry for neon sign manufacture or air conditioning servicing it will probably have seen much heavier use that if it was used in a school science laboratory.
* If the seller has a vacuum gauge available, ask them to measure the pump's ultimate vacuum.
* Inspect the oil. Is it dirty? Metallic particles in the oil may indicate heavy pump wear. Vacuum pump oil is usually colourless and doesn't smell. If it smells it's the wrong kind of oil.
* Unscrew the oil drain and let a few drops run out. Is the oil contaminated with water?
* Listen to the pump running. These pumps are usually pretty quiet. Clacking noises may indicate sticking vanes.
It seems from what Harry says that you should be fine with a mechanical pump for making neon signs, although you will need to be able to manufacture and seal the glassware. Perhaps Harry could confirm if a single stage pump is adequate or if a two stage pump is required?
Hope this helps
Chris
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And probably in better condition as it was used recently and when it was used it probably worked. Unuse is worse for a pump than use. Every pump I got from a school was is poor condition because they never use them enough or change the oil.
I've never seen a HVAC pump at the pawn shop that had dirty looking oil in it. They were all working just fine before getting lifted. Stuff at schools sits around and rots forever.

Getting an oily smoke/mist out of the exhaust when it's pumping down with a covered up inlet is a good sign it's sort of working.

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Cydrome Leader wrote:

it probably worked. Unuse is worse for a pump than use. Every pump I got from a school was is poor condition because they never use them enough or change the oil.

They were all working just fine before getting lifted. Stuff at schools sits around and rots forever.
Obviously there's a difference of opinion here. I personally don't see that there's much harm that can come to a pump if it's left unused, provided that it doesn't contain water and that it isn't left with the inlet open so that it can fill with dirt. It's just like leaving an engine filled with oil for years; I don't think it will do any irreparable damage. One pump I had from a laboratory which had been standing for a year or two (and DID have some water in it) was a bit stiff at first but after an oil change and a few rotations it was fine. When I dismantled it there wasn't any appreciable corrosion either, just a very slight discoloration where the rotor had stopped. I think abrasive dirt is probably the biggest cause of pump damage. But in general these belt-driven pumps are very rugged and reliable.
Chris
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You missed the most important one: attempt to determine if the pump has been used with any toxic substances in its former life. This is hard to do, but some common tip-offs include:
Off-board oil filtration devices
Inert gas feed for purge or ballast
Residue around the intake or exhaust ports
Former owners include medical, or laser users
By all means, *ask* what the pump was used for, and ask who owned it before the present owner, if that information is available. Any fishy answers would be grounds for me to pass on the item.
Jim
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jim rozen wrote:

Good point Jim. I should have remembered that one!
Chris
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Chuck Sherwood wrote:

If you turn the pump over by hand, one in good condition makes a distinctive sluurping noise. Of course, if you haven't heard it, this may not help.
Steve
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Cydrome Leader wrote:

the motor. Not using a pump (letting it sit with old oil) seems to be the worst thing you can do to it.
Interesting. I got a two stage pump with a burnt out motor free from the Cavendish Laboratory. Probably the motor had burnt out because of a faulty oil distributor valve in the pump, which allowed the pump chambers to fill with oil and stalled the motor. I got the motor rewound and replaced the pump seals and it's a good pump. I've been lead to believe that this isn't uncommon on pumps which don't have a thermal cut-out fitted to the motor. Badly damaged pumps are most likely the result of water being drawn into the pump (and being allowed to sit, causing corrosion), or abrasive dirt causing wear.
Chris
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I have two 1/3 HP direct drive vacuum pumps that I am about to throw away. Chicagoland.
Both pumps do NOT work well. They both spin, but do not suck.
I know exactly why. They rusted solid and could not spin, when Ibought them. I took them apart, cleaned etc. Now they spin but produce almost no vacuum.
If anyone needs them, for the motors or whatever, let me know. I can post more details if anyone is interested.
i
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FWIW, I bought a vacuum pump from William Noble who posts on this BB occasionally. I use it for a vacuum chuck I built. I don't know if one of the pumps he has will meet your needs, but I found William to be a help. The pump I bought pulls about 25 in and works well. Quiet little thing too.
http://www.wbnoble.com /
Peter

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snipped-for-privacy@w-sherwood.ih.lucent.com (Chuck Sherwood) wrote:

Take a look at the gast pumps, they seem to be much lighter, especially the oiless rotary vane ones. Shipping seems to be around 25-40. What you need sort of depends on what you want to do with it too. You can get all of the max vac and flow rate information for the gasts out of their on line info (some times you have to dig a little and figure out their catalog # systems) jk
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On 13 May 2005 16:00:04 GMT, snipped-for-privacy@w-sherwood.ih.lucent.com (Chuck Sherwood) wrote:

A Refrigerator Compressor Vacuum Pump http://www.sas.org/E-Bulletin/2003-12-12/labNotesAS/body.html
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca
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| My 11 year daughter is showing a strong interest in science. | We received a Edmunds catalog with lots of cool stuff in it. | | I have always wanted to play with vacuum stuff when I was a kid | and I didn't get much of a chance so I figure now is my chance. | | I figure it would be cool try to make a crude light bulb inside | a bell jar and things like that. | | I looked at ebay and there are many vacuum pumps FA. | | Do I need a two stage pump and how big of a pump do I need? | The killer is these things are heavy and shipping is expensive. | | chuck
I guess it ought to be asked if you have an idea of what kind of volume, flow, and vacuum level you intend to work with? Light vacuum, up to about 29 inches of water or more and great volume and flow is available from your household vacuum cleaner. Find surplus vacuum blowers and you can get to 90 inches of water. With a large volume system you first empty it with a high volume pulp like the mentioned blowers then you close that system, switching to a slower pump. HF sells one or two, one being an air operated one that is for A/C systems. No vacuum draw is given, but I assume the A/C guys know what it should be. Above that, then you start looking at lab pumps. Available in all sizes, flows, and costs, so you need to quantify what your needs/desires are first.
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I was always interested in messing around with vacuum, but I know better, I have way too much stuff going on as it is. Hope you guys have fun with it.
A crude light bulb is pretty simple to make. Use a piece of iron wire (a single strand from picture frame wire works nicely) between two nails in a cork. Wire the filament up to a transformer. Drop a light match into a baby food jar and immediately put the cork in place. When the match goes out, turn on the voltage.
What you need to do is get rid of the oxygen, not pull a good vacuum.
I saw this demonstrated in 5th grade, and had to try it when I got home. My dad helped and thought we should turn off the lights, since it would be pretty dim. I just missed one piece of the setup--the transformer. We plugged it directly into 110VAC. Really nice flash.
Steve
Chuck Sherwood wrote:

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My son and I did just the same experiment 4 years ago with great results we used different inert gasses like argon, helium

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I managed to get the welch 1400 pump off ebay for $130. I picked it up last night and it looks good. The seller stated that his father owned it for AC work but stated he never saw him use it. The inlet had AC fittings on it (and was capped) so it appears it was used for AC work.
I have no way to test it, other than putting my finger over the intake and observing that it does suck. The noise changes considerably as the vacuum is built up. Opening the gas ballast also increases the noise a lot when the input is capped.
This pump should work much better than a converted AC compressor and was a turn-key operation for 130. can't beat that!
I will probably pick up a cheap automotive vacuum gauge to get a rough idea if its working well.
thanks for all the help chuck
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A bourdon tube gage won't really tell you what's going on, see if you can hunt up a thermocouple gage. These read down to about one micron and will tell you if the pump is working up to what it should be doing.
Jim
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I have read a little about these on one of the laser web sites. Any recomendations where to get a good one ? chuck
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Chuck Sherwood wrote:

Good luck with the experiments. I'd be interested to see some pictures sometime!
Chris
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