Vacuum pump choice

[massmanute]

I am collecting parts for vacuum/pressure pot setup for blank stabilization and or casting.

What kind of vacuum pump is more desirable, a venturi-based pump or a displacement pump?

I have a spare vacuum pump I had scrounged a while back. It is a small Gast brand piston pump. However, I read somewhere that the solvent vapors from stabilizing and/or casting solutions can damage the parts in displacement pumps. Is this a realistic worry? If so then maybe a venturi-based pump might work better. I have a compressor I could use to power a small venturi-based pump, so obtaining a compressor is not an issue.

Being partly of Scottish ancestry, I should say that cost is an issue.

 

[snyiper]

Ok I am of Scottish ancestery, why would cost be a issue...LOL Dont worry I take no offense just havent heard this explanation yet.....It could explain some things ...LOL you can PM if you prefer.

 

[snyiper]

Ok I am of Scottish ancestery, why would cost be a issue...LOL Dont worry I take no offense just havent heard this explanation yet.....It could explain some things ...LOL you can PM if you prefer.
To answer your question I use a Gast Vacuum pump and used it for trying to stabilize wood with Plexitone and it had no ill effects on the pump.

 

[LEAP]

I've used my Gast vane pump for stabilizing and casting with no problems. I've since set it up for vacuum chucking on the lathe so bought a little venturi from Harbor Freight, it works just fine as long as you have a compressor that will supply a good air flow. My little construction size compressor was not enough. I've since bought an industrial sized compressor and can maintain 25" of vacuum in the paint pot using the venturi.

 

[Padre]

Lang lee Scootlund!!

I second Phil on the HF venturi. It works great, and with the 20% off coupon it's even better!

The other thing to remember is that acetone and other solvents will eventually eat out the rubber gaskets on a vacuum pump. You can get replacements fairly easily and inexpensively, but it is another cost to consider when you are buying a considerably costly pump.

 

[PTownSubbie]

+3 on the venturi. No damage possibilities from the acetone to a pump. I have a pump but don't use it for stabilization with Plexi-tone solutions.

 

[massmanute]

Thanks for the answers so far.

How much compressed air does the Harbor Freight venturi pump require in real life? The catalog listing for the venturi pump says it will operate on 4.2 scfm at 90 psi, but I have heard that in actual operation it requires much greater air flow, maybe twice as much.

Also, I have a harbor freight compressor that is supposed to supply 4.9 scfm at 80 lb, but I suspect that the specification is optimistic.

If, as I suspect, the specification of both the venturi pump and compressor are optimistic, it seems unlikely to me that my compressor is beefy enough to drive the venturi pump. If this is the case then maybe I should look for another venturi pump, which would be unfortunate because most of them are more expensive than the harbor freight unit.

Any comments?

 

[Padre]

I never actually measure it, but I have a 60 gallon 3hp Kobalt compressor that keeps up with it just fine.

 

[massmanute]

I ended up buying a different venturi pump off an ebay listing.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350417512657&ssPageName=STRK:MEWNX:IT

It is a used unit, Vaccon model JS-90M. A fairly complete set of specifications are available at the vaccon.com website.

http://www.vaccon.com/perf-j-mid.aspx

This model is specified to draw 1.8 scfm at 80 pounds pressure for the driver gas, which should be well within the capabilities of the compressor I will be using. The maximum pumping speed at zero inches of mercury vacuum is 1.2 scfm and the ultimate pressure at 0 scfm is 28 inches Hg, which according to the graphs is optimal at 85 pounds of pressure for the drive gas, and at 80 pound of drive pressure the ultimate vacuum is very very close to 28 inches mercury.

Looking at the pump down curves for this and related models, none of which exactly match the system I am building (2 1/2 gallon tank) I think it would take about 8 minutes to pull it down to 26 inches of Hg, which is probably about the level at which I would be pumping mostly solvent vapor rather than air.

I think this performance level would be reasonable. In some ways they might even be better than a faster pumping rate because the slower rate would mitigate the danger of excessive foaming when pulling vacuum. Of course at my altitude of 4300 ft above see level all these vacuum figures would be somewhat different, but at least these specifications and estimates provide a rough idea of what to expect.