Abusing compressor as a vacuum pump

Hi
Since long I've been guessing where I could get a vacuum pump for little money. I need it for casting.
Just now, an idea popped up in my head:
If I connect the compressor's intake to some hose, and keep the compressor running, I will have vacuum at the intake. Well, it won't be the most energy efficient solution, but for rare use I think it's OK.
Is this idea stupid, funny, brilliant or what? What are your arguments against this idea?
Thanks for your input. Nick
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Yes, it will work, but it won't pull a very deep vacuum. Probably good enough for casting though. Make sure you filter the inlet to the compressor though as any solids will destroy it pretty quickly. Change the oil after its been used as it may condense a fair amount of water vapour,which might get into the oil.
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I have not seen the set-up you are proposing, not helpful I know.
how about this:
You can pick up a venturi for short money which pulls a vacuum using shop air. You need to be mindfull of leaks in your vacuum system otherwise your compressor will run constantly.
good luck, Andy
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Building your own vacuum pump http://www.dream-models.com/eco/vacuumpump.html
Eferg

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HF sells a venturi-based vac pump for $9.99 Noisy but it works.
- - Rex Burkheimer WM Automotive Fort Worth TX
Nick Mller wrote:

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That's interesting, what % of air does it remove?
i

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message wrote:

According to the box, an "ideal vacuum"!
Might be OK for evacuating vehicle cooling systems though-in fact, I have a Blue Point setup I use at work. Pulls to about 22-24 inches Hg...
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Ignoramus23776 wrote:

I don't know, but it's sold for A/C work, so it should be able to pull a decent vacuum. Not that this is a copy of a design sold by Four Seasons and others in the mainstream A/C aftermarket. I have one I bought just to see what it was, but I've never really used it. I can testify that it's way to noisy for my tastes, probably consumes a lot of CFMs.
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Do they ship to Germany? :-) Sounds strange, but I never came across a ventury pump (either water or air) here. Well, you get some, but they cost 10 times what HF wants.
Also, I guesstimate, that I get about 100l/min of "sucction", because my compressor has nominal 300l/min.
Nick
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[I tried it on my compressor, but it didn't pull enough vacuum to debubblize investment. That requires enough vacuum to boil water at room temperature (about 29" Hg). The result was worse than no vacuum at all - bubbles everywhere. If all you want to do is suck on the bottom of your flasks to get the metal to flow in, you don't need as high a vacuum, so this might work for that.]
Andrew Werby www.unitedartworks.com
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Sad. :-( OK, that for, I need more vacuum but little flow.

This was the primary intention.
Thanks for sharing your experience.
Nick
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I recently bought a couple vacuum pumps off ebay. One was a nice Welch 1400 pump for $140. It was used for Air Condition pump down.
I also bought a welch 1405 pump that was suppose to be freshly "rebuild" but I'm pretty sure it was just "freshly repainted" to make it look good because the oil was dirtier that dirt. It still pumps well so I kept in anyway. It went down to 40 mTorr with a crude plumbing so the pump seemed to be working. Full atm is 760 torr and it was pumping .040 torr, but it should easily do .010 torr.
The welch 1400 didn't do as well but the plumbing was even worse, so it wasn't a fair test.
Anyway there are lots of vacuum pumps FS on ebay. chuck
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On Mon, 11 Jul 2005 14:37:52 +0200, snipped-for-privacy@gmx.de (Nick Mller) wrote:

An old refrigerator or dehumidifier compressor will pull about 26" (660mm Hg) of vacuum. Two of them in tandem will get down to about 27, maybe 28 in Hg. Mine does (do) anyway, YMMV.
The HF venturi claims 28.3 in Hg at sea level. What's inside the box is just a 2" x 3" x 3/4" block of aluminum with three holes drilled in it and a couple of brass fittings. If you have a lathe and a drillpress you could make one quite easily. If you're curious, email me. I'd be glad to take mine apart, take some photos and make some measurements. Note: I'll be offline for a few days starting later this week.
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On Mon, 11 Jul 2005 22:12:32 +0200, snipped-for-privacy@gmx.de (Nick Mller) wrote:

Dimensioned sketch on the way.
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On Tue, 12 Jul 2005 09:56:47 +0200, Nick Mller wrote:

Nick or Don, could you please post this info in the dropbox?
Thanks!
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Is it OK if I build it in the next days and put the drawing + pics on my HP? I'm not familiar with the drop-box, also Don has the (C) for the drawing. :-)
Nick
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On Tue, 12 Jul 2005 20:46:17 +0200, Nick Mller wrote:

Yes, please do. I'd like to see how yours turns out. I'd also like to hear how you bored that tapered hole for the air exhaust.
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See my other posting. It is finished, but I have just 2m of tube to test it. It's pulling these 2m of water easily (and makes a wounderful mist), with 2 bar (30 psi) on the input side.
The tapered holes: Well, you need to make two conical D-bits out of drill rod. Not to complicated if you have a lathe. I also made some changes. Basicaly, it is out of hex stock (aluminium) that did the job and looks good. On the air inlet side, I modified a quick release fitting for compressed air (don't know how this is called) so that it also forms the jet. And on the vacuum side, I pressed in some brass tube.
Wait 'till tomorrow. I'll keep you informed (have to buy longer tube) with pics and plans.
Nick
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