El cheapo rotary vane vacuum pump

Might they be diaphragm pumps? Those are more popular than vane pumps, for fronting turbo and ion pumps and such.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

For mechanical pumps I think it's all about the vapor pressure of the pump oil. You can buy "industrial" stuff, fairly cheap. A good pump with good oil does better. There's a guy.. builds medical equipment, wrote a book with his daughter about physics experiments, they took a Robinair pump, put good oil in and got to ~10 mTorr. IIRC Series is not going to help. In parallel you get more pumping speed.

George H.

For mechanical pumps I think it's all about the vapor pressure of the pump oil. You can buy "industrial" stuff, fairly cheap. A good pump with good oil does better. There's a guy.. builds medical equipment, wrote a book with his daughter about physics experiments, they took a Robinair pump, put good oil in and got to ~10 mTorr. IIRC Series is not going to help. In parallel you get more pumping speed.

George H. =============================================================

Harbor Freight sells single and two stage pumps, where internally there are two pumps in series. The single stage pumps will base out in the vicinity of 1 torr, and a good two stage pump (not sure if HF's will go this low or not) will get to less than 10 mtorr, given oil with a vapor pressure lower than that at the operating temperature. Years and years ago the cheap trick for vacuum pump oil for vane pumps that didn't need the absolute best base pressure was to use Mobil 1 synthetic motor oil. Fuzzy memory says that the

5w20 motor oil works out to about the right viscosity at a normal pump operating temperature. However, Mobil 1 has changed formulations at least twice since then so can't say if it will have a good enough base pressure nowadays or not. You can always ballast it for a day or three to let it remove the volatiles by itself. Plenty good enough for solvent drying and water removal in things like freeze dryers and gel dryers, where water tolerance is paramount and the base pressure only needs to be about a torr.

Diffusion pumps and real turbomolecular pumps need backing pumps that get below a few hundred millitorr so two stage vane pumps are standard. They also build hybrid turbo pumps where they have the usual turbomolecular stages and then a few turbodrag stages which let them work with foreline pressures up into the 1-5 torr range where multistage diaphragm pumps can reach. That is nice because it lets you get rid of the oil, for less system contamination, but usually the ultimate base pressure is not as good (10-8 torr instead of 10-10 torr).

Regards, Carl Ijames carl.ijames aat deletethis verizon dott net

I looked at a dead one someone here had bought from overseas, appears ident ical to the Harbor Freight version. It's single-stage rotary. There's app arently a 2-stage version too, $200, claimed 25 millitorr.

But be warned, if this one jams (or perhaps just runs slow,) its starter wi nding turns to charcoal. It'll still work, if you grab the cooling fan an d give it a spin! In the right direction of course.

Perhaps make your own somewhat-gassy DIY vacuum tubes, wo/needing kilobucks of pro vacuum system. Or get every last bubble out of your oil-tank DIY high volt transformers and caps.

Recently Salvation Army stores here have been filling up with vacuum chambe rs.

They're these 8" heavy polycarb cylinders, with a white dome lid and a smal l grey rubber button to vent. Used with a "Food Saver" or "Snail Corp" bag heat-sealer. I don't think those bag sealer pumps can even do half an atm osphere. But they might work better than the Harbor Freight pump, where t he pump oil would fill with water and rust, if we try using it for dessicat ion or freeze-dry.

(((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))) William J. Beaty

beaty, chem washington edu Research Engineer billb, amasci com UW Chem Dept, Bagley Hall RM74 x3-6195 Box 351700, Seattle, WA 98195-1700

On a sunny day (Wed, 15 Apr 2015 13:51:33 -0700 (PDT)) it happened Bill Beaty wrote in :

I got an email from airmiles that I needed to use those else they went void. So I bought a food vacuum machine for free. I just wonder if I can make a vacuum tube demo with a broken light bulb and some plate and grid in a transparent food vacuum box. It is a nice machine, vacuums and seals plastic packages too.