Fusor Forums

Yes, it starts at atmospheric pressure and then slowly drops. I generally wait until the thirty minutes is up to check the gauge after it has had sufficient time to heat up, but I'm pretty sure it gets down to near its lowest pressure immediatetly.

I had my eyes on this pump for sometime:
https://www.ebay.com/itm/EDWARDS-5-ROTA ... SwQS1aQn4L

It's a bit pricey but I'm sure I could negotiate.

That is a good price a working 5CFM Edwards.

Richard Hull

Oddly enough, it's supposedly on 3.75 CFM, but is rated to reach 7.5 X 10^-4 Torr. I figure that will be enough to back a diffusion pump.

Checking the specs, the 5 in E2M5 model is 5 m^3/hr pumping speed which I convert as about 3 cfm.

Sorry, I forgot Edwards is Euro and thus SI. Still, it is good enough for a fusor, if in good shape.

Richard Hull

That appears to be a good pump and will certainly work with any DP as long as it gets below 50 microns; so when you say

but is rated to reach 7.5 X 10^-4 Torr. I figure that will be enough to back a diffusion pump.

So, as long as it gets under 5 microns (assuming the system has no real leaks) you will be more than fine.

No mechanical pump (even new) will really do that sub-micron - I have a very large pump, a leak proof system (and back fill with dry air), and 2-3 microns is what it can do and that is excellent for most mechanical pumps.

IMHO, a mechanical pump is doing well to get into the single digit micron range.

I knew not to expect it to reach that pressure. I learned not to expect things like that from my HVAC pump. Anyways, the Edwards pump is here now and, of course, I can't find anyone selling adapters from 1 bsp to kf25 that doesn't ship from Hong Kong.

Anyone with a lathe some brass tube and a little brass plate would make one in under an hour
no oxy acetylene no prob just soft solder will do.

MAKE ONE!!!!

Bob and John are correct.

A used pump is doing fabulous if it easily hits 15 microns within a minute or two at the head. If it goes below 10 microns, it was well cared for or not used much in a good environment.

Where there is a will there is a way. KF Adapters can be whipped out quickly by even a novice machinist. Made in brass, they are easily soft soldered.

I have had to do this a number of times back in the 1990's as I used a lot of HVAC pumps. Some good and some not so good. The worst ever did hit 30 microns rapidly. The best was a 5 CFM yellow jacket that hit 12 microns at the head in under 40 seconds! Now, I use only belt drive pumps which on whole are no better or worse in evacuating a system but are much, much more quiet and easy on the nerves, easy to repair and replace motors.

Richard Hull

I managed to rig up an adapter. Unfortunately, it takes the inlet down to a 1/4" at one point, so I still plan to replace it do to how much that will bottleneck the pump. The second problem is the oil. The people who sold me the pump weren't quite the brightest and decided to leave the oil in the pump while shipping it despite what I told them. As you would expect, the box arrived on my porch covered in oil. As far as I can tell, all the oil drained out. Would it be okay to use some of my Robinair pump oil with the Edwards pump? It's fresh, but it might not be compatible. As far as it's "type" (such as hydrocarbon), it doesn't say. Here's the link to it: https://www.amazon.com/gp/product/B000X ... UTF8&psc=1.
Thanks!

-JO

you can get the right ultra grade 19 oil here
http://www.pchemlabs.com/product.asp?pid=1438

Not long ago I ran the pump for about 3 minutes and got down to 500 microns (that's with little oil and npt threads). I was shocked at how quiet it is and the pressure it reached quickly. Definitely an upgrade from my HVAC pump.

While 500 microns is terrible for a good pump, that it had little oil can explain that figure but also, an excellent way to destroy the pump. Always fill the pump to the correct level before operation.

I understand this, but I won't have any proper oil for it for at least another 10 days. I need to get some tests done, so I asked if I could use the robin air oil. I understand it's not the official oil, but it would only be temporary. Does anybody know for a fact it would be acceptable to use the robin air oil? Thanks!

Direct drive oil is direct drive oil and as long as your Robinair oil is fresh from the jug it will suffice until your 19 oil arrives. Try it and see what pressure you hit at the inlet of the pump.

Richard Hull

There is one difference: Pfeiffer pumps use moderately higher viscosity oil. I doubt it matters.

I’d worry more about the vapor pressure of the cheap oil and the implications of using it in your newly purchased pump.

As long as you are prepared to properly clean out the pump - remember, that is no simple task to really remove the wrong oil if its vapor pressure may be a future issue - then fine. The oil will provide the pump lubrication to enable you top test its operation. However, might be easier in the long run to just wait and use the proper oil; certainly less work.

It will pump or it will not pump regardless of oil. This is not a new pump. Remember it was bought from a guy who shipped it with oil in it. Not a real vacuum head who owned it last. No good vacuum head ships a pump full of oil.

Richard Hull

I've ordered the proper Ultragrade 19 oil from Amazon and it's estimated to get here Wednesday at the soonest. I currently plan to wait until it arrive, but I'll let you know if I decide to test it out with Robinair's premium oil.

The oil arrived today and I filled the pump up to it's max value (I added a tad bit too much at first). I then turned the pump on and gave it 10 minutes to pump down. I came back to the same results I received without oil: 500 microns. So, in preparation for another test I added more Teflon tape to my adapter and tightened it until I was confident it was sealed. I've also been letting the pump sit for a bit so the oil can flow into the gears and such. If anyone has any suggestions as to things I should do before testing again they would be much appreciated. Thanks!

Try running with gas ballast open for 15 mins and then closed for an hour. Then repeat once and report for findings. Also include a pic of your test setup. Make sure you’re in a well ventilated area to protect your little lungs.

Are you just pumping on the vacuum gauge? A decent pump will never pull just 500 microns; either you have a massive leak - i.e. a bad o-ring or non-vacuum tight connection between the gauge and pump body (Also, have you tried listening for a leak?) or water in the pump (so Bruce's advice will help there.)

It would help if you provided a photo of your setup with the gauge/pump connection system in detail. Also, is your pump oil now discolored? Maybe a photo of the oil level site glass.

Running without the gas ballast makes an awful noise. Are you sure this won't damage my pump?