Page 1 of 2

Vacuum Pumps, can it be good AND cheap?

Posted: Wed Mar 07, 2012 4:12 am
by Rob Pope
OK, I'm a senior in high school who's been wanting to build a fusor for quite some time.
From what I can tell, there are going to be two major financial roadblocks, a high voltage power supply, and a vacuum pump.

I've been trying to look at information about pumps, but there is seriously so much out there. Without experience (which is costly) I don't know exactly which route is best. From what I can tell, rotary vane is the best, but I don't know this for sure...

Also, when looking at prices, I will see apparently the same thing going for anywhere from $200-$13,000

How can I tell what is cheap, what is crap, what is high maintenance, what can take the inevitable abuse of a novice who knows nothing about vacuum care (other than it needs oil), and what is just a rip off?

I could use any help you guys can offer regarding this, keeping in mind that price is really a limiting factor.

Thankyou

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Wed Mar 07, 2012 5:41 am
by Conrad Farnsworth
You can get good pumps that are cheap. I'm sure if I wouldn't have completely disassembled one of my epay pumps I could have gotten it down to diffusion pump pressures.

viewtopic.php?f=25&t=4060&hilit=faq+-re%3A+faq#p21468

Read that FAQ if you do buy a used one. It will save you a bunch of time and money!

Also, check the specs on all of the cheap pumps. Generally you want 100 millitorr of less of vacuum.

Good luck!

-Conrad

P.S. I used our school's vacuum pump to get my first demo mode pump down you should try asking them.

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Wed Mar 07, 2012 7:53 am
by MarkS
Hey Rob,
Any of the Welch DUO Seal pumps will be quite sufficient for you needs. A brand new single stage duo seal may actually be able to get you down secondary pump pressures (sub 100 micron). A brand new one is quite costly however. You're going to be better off with a 2 stage one. I personally own a 1970s welch 1406 duo seal pump which I got ebay for about $100 and rebuilt it with a kit for another $60 or so. When I got my pump apart it was covered in fine coat of rust on all the internals, the vanes were scored, and the seals were questionable yet it still pulled down to 100 microns, and could quite easily pull the skin off your hand. Initially after the rebuild and break in period the pump was pulling down 1 micron or so if I remember correctly . After 4 years of storage I pulled the pump out tonight and it's still pulling down to 100 microns. I think the extra 99 microns are from water in the oil or possibly a leak in my chamber (im guessing the latter). If you can't tell I'm a welch fan through and through. Any used pump may be a decent pump, but pulley driven pumps and welches in particular last forever. When buying used look out for rust, make sure the motor and base come with the pump itself, and steer clear of pumps which were used for pumping dangerous chemicals like hydrazine. Most pumps have a relatively cheap rebuild kit which will replace the seals, the belt, and most importantly the vanes/vane assembly. I would steer clear of the high speed pumps because they have more wear and tear on the moving parts and are built more cheaply. If you're going to buy new I would look at cheap refrigeration pumps, especially on Harbor Freight's website. I was xmas shopping there and saw a two stage high speed refrigeration pump on sale for $125 BRAND new and just about started drooling. Be warned though if you get a refrigeration pump you're going to have to solder a vacuum worthy flange onto it, or use a rubber hose to connect it to your vacuum manifold.

FWIW I got my pump for my fusor project in my senior year of high school (class of 2008) and its probably my favorite piece of lab hardware. Good Luck!

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Thu Mar 08, 2012 3:40 pm
by Rob Pope
Thank you both for the advice
I read the FAQ and found it very useful, I'll remember to use it when I get my first pump.
I'll start looking for a belt driven pumps, and I'll be sure to remember the performance of your Welch

Now I need a gauge

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Thu Mar 08, 2012 11:23 pm
by Rob Pope

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Thu Mar 08, 2012 11:43 pm
by Jim Kovalchick
Rob,
In my role as chief scrounger and financier of my son's project, I have learned that nothing associated with a fusor is cheap unless you're patient. You are right, the vacuum pumping system and power supply can be big ticket items, but each of the following can also be multiple hundreds each:
deuterium
high voltage feed through
neutron detection
chamber view port
geiger counter
main throttle valve
vacuum pressure indication
lecture bottle regulator

Some of the other stuff adds up pretty quick too. Stainless fittings including needle valves, vacuum chamber seals and fittings, vacuum pump oil, high voltage cable, depending on your power supply: diodes, ballast resistor, voltage divider, panel meters, and the list goes on.

Almost everything we bought was used and even then it wasn't always cheap. We were on a timeline so sometimes we bought when we needed something not just when something cheap came up. Ultimately I earned a 'blue star' on ebay. One trick I used was to search generically by lot. Use "vacuum lot" or "swagelok lot" Sometimes I found groupings of multiple items that were cheaper than buying by the eaches. The best example was a search of "vacuum lot" that resulted in a working turbo pump and controller, working thermocouple gauge and indicator, working granville phillips ion gauge controller and multiple stainless conflat and KF fittings all for $500. We still pick stuff out of that box to use.

Good luck to you on your quest. If time is on your side, you can pick up some bargains.

Jim K

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Fri Mar 09, 2012 12:24 am
by Carl Willis
And don't forget to search locally. Check Craigslist for vacuum pumps; they're surprisingly common in all kinds of applications. I bought a Craigslist one here in Albuquerque a couple years ago, a nice direct-drive pump in good condition. And of course I could drive over, check it out on the spot, and pay cash at a bargain price, with no shipping charges to boot.

There's no guarantee that an individual pump is in good shape, but I'd guess this one is decent. The seller reports that the pump runs and it pulls a vacuum. You'll certainly have to fill with new oil, and possibly replace some worn seals. But the Welch Duo-Seal line of pumps are very reliable with which lots of fusioneers are experienced.

-Carl

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Fri Mar 09, 2012 2:42 am
by Rob Pope
Thank you all
I'm currently watching that pump and a couple others, does anyone have any experience with yellowjacket direct drive or cenco brands?

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Fri Mar 09, 2012 1:44 pm
by Rob Pope
Hmm, I origionally thought that this unit was dual stage, though uopn further research I realize that the 1399 is a single stage unit. Will it still be suitable for fusion?

Re: Vacuum Pumps, can it be good AND cheap?

Posted: Fri Mar 09, 2012 2:59 pm
by Richard Hull
I own two yellow jacket 5 cfm pumps and one was my first fusor I and fusor II pump. They are good pumps and have no trouble hitting vacs below 20 microns if in good shape.

I still prefer a belt drive, and within that context, only a Welch duo-seal, though I have used a 5CFM belt drive Precision pump for the past 8 years. If I ever put my foot in the path to do fusor V, I will use one of my giant 1397 welch belt drive pumps that have been languishing around the lab.

Richard Hull