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Help me in my baby steps in the vacuum world.

Posted: Fri Feb 05, 2021 10:18 am
by Cai Arcos
Hello:

I've recently started my journey into the vacuum world. Having absolutely no experience whatsoever, my first step was to fully digest the FAQs, read some literature and then to buy a tested MKS901p gauge.
A friend of mine who makes neon lights for a living kindly gifted me an old vacuum pump that was untouched since nearly 10 years (¡thanks Leo if you are reading this!). I attach a photo of the pump in question. As you can see. its of the "belt type" variety, but has no markings nor models.

The original motor had a large leakage current to ground, so it was replaced with another triphasic motor of similar characteristics right away. This is no big loss, since in the end I will have to use a monophasic motor in order use the pump at my apartment.

I also attach a photo of this first set up. The gauge is connected using a really thick plastic tube pretty much directly to the inlet of the pump (there is around 1cm max of space between the inlet and the gauge). Using the original oil (which also is not full, but seems to be at half level), the best I get is around 1 Torr (even after leaving the pump on for around 30 mins this reading does not go lower or higher).

Now, I'm aware that my tube is not ideal for this application, but I'm sure that theare are not any leaks, because after turning off the pump the vacuum the pressure rises only slowly, and also using water and soap does not show any leaks.

According to the FAQs, what I should do now (what I should have done!) is change the oil in the pump. But, because there are no markings, I have no idea what the original manufacturer recommended (which is what is recommended in most threads). Now, in reading Vacuum Equipment and Techniques by Guthne and Wakerling, it is stated that:

a) The SAE number of the oil should be between 15 to 20.
b) Temperature range "not very great"
c) Viscosity index is not critical.
d) Lubrication is essential.

All the oils I've seen are specified by two numbers (for example 5W-30). According to Wikipedia, the first number referes to the oil index when "cold" and the second one when "hot". In the Appendix E of the same book various types of oils commonly used are recommended (I attach the photo). Using a conversion table (http://www.nadi.it/english/viscosita.htm), I find that the extremes of usable viscosity indexes are 40 and 5 (in SAE automotive units).

Thus, I should be able to use a common 15W-40 oil, right? Here is where I look for input from more experienced members of the board!

Re: Help me in my baby steps in the vacuum world.

Posted: Fri Feb 05, 2021 4:46 pm
by Richard Hull
You must buy special belt drive pump oil!!!! about $50 per gallon. drain the oil oil immediately and report what it looks like. I cannot for the life of me figure out how you used soap and water to find leaks in a vacuum system!!! You need to use alcohol or acetone and then only sparingly. It you suck water or soap into the system you will horribly foul and ruin your oil!! You must not have read the FAQs that closely. At no point is soap and water recommended to find leaks in a vacuum system. They are used in high pressure seal testing only. (finding pin hole leaks in tires and inner tubes.)

Richard Hull

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 3:16 am
by Cai Arcos
Richard:

I understood that some type of special oil would be needed, but what is most often recommended is to use the one recommended by the manufacturer, which I don't know. Is there any generic brand I could use?
Regarding soap: this was an idea that had a friend of mine who works semi regularly in high pressure stuff. But you are correct, it does not really seem like a great idea know (specially when in the book I quoted they go to great lengths to talk about oil contamination by water...). My fault.
The pump is at work now, as soon as I can I will empty the oil and report back.

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 5:15 am
by Maciek Szymanski
There are super expensive, very low vapor pressure oils offered by vacuum companies like Varian or Leybold. And a lot of generic vacuum pump oils for industrial use (milking, vacuum packaging, handling, HVAC). Until you don’t expected your pump to work on the limit of it’s performance (and this requires it to be in perfect condition and is not the case for the backing pump) the industrial grade oil will do. Just search for “vacuum pump oil”.

BTW your pump looks like it’s a piston pump. After such long period of storage there may be a problem with the valves - the oil residues may prevent them from closing completely.

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 1:38 pm
by Cai Arcos
Maciek:

Thank you very much for your reply! Can really any tipe of industrial oil work? Is it "that easy" for a first try with a roughing pump? For example, would this oil from Amazon https://www.amazon.com/Octopus-Aceite-B ... 644&sr=8-5 be adequate? From this listing, it seems like compressor oil is "the same", but a quick searching on the internet seems to reveal that this is not true.

Regarding the valves: it might very well be the case. However, this being a freebie as well as my first steps in the vacuum world as well as for what I intend to use it, 50-70 microns should be plenty. Could this be accomplished with the valves in a bad condition?

Once again, thanks for the help. I tried to read and ask the people around me about this stuff, but I really am a neophyte without practice and a lot of of things fly over my head.

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 1:46 pm
by John Futter
Pump looks like a two stage rotary vane type to me

good find

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 5:00 pm
by Maciek Szymanski
For first tests I would try any inexpensive industrial vacuum pump oil like Total Agritraite 68. Or this one:

https://www.ebay.es/itm/ACEITE-BOMBA-VA ... SwJ9VdrzkT

Regardin the piston/rotary question - for me the shaft is located too low and the round part of the housing is very small diameter to me for the rotary pump, but I’m not 100% sure.

Re: Help me in my baby steps in the vacuum world.

Posted: Sat Feb 06, 2021 9:59 pm
by John Futter
oils with low vapor pressure are what is needed there are low foaming mineral oils like tonna T25 /238 etc the later figures relate to viscosity.

the above oils are Shell but any oil company expert will cross reference these for you i have done that to Mobil oils but cannot remember the Mobil codes

Re: Help me in my baby steps in the vacuum world.

Posted: Tue Feb 09, 2021 10:14 am
by Cai Arcos
Today I was able to extract the oil from the pump. I attach a photo.
As you can see, the oil is very dirty and is probably the reason the vacuum was so poor. Luckily, there are no metal chips or fragments.
As soon as I can I will purchase new oil and do new test runs.

Re: Help me in my baby steps in the vacuum world.

Posted: Tue Feb 09, 2021 3:53 pm
by Richard Hull
If that image is all the oil you got then the pump did not have enough oil in it beyond keeping it from locking up. Most pumps will take a large fraction of a liter or more of oil There should be a sight glass for oil level observation.

Richard Hull

Re: Help me in my baby steps in the vacuum world.

Posted: Tue Feb 09, 2021 11:26 pm
by John Futter
try to find a manual for the pump

who made it??
it that a sight glass on the opposite side from the pulley?? the oil level should have been visible there

Re: Help me in my baby steps in the vacuum world.

Posted: Wed Feb 10, 2021 3:50 am
by Cai Arcos
Richard, John:

The oil was a little bit over the half mark in the viewer. I still turned it on because it rotated freely when turned by hand.

Regarding the manual, or who made it: I have no idea!!
The only specification is a little placard that I attach below. I've spend quite some time searching for the model online (OD.10 or 0D.10) with no luck. The manufacturer is not specified anywhere. The motor that came with the thing has a placard from an italian motor making company. I strongly suspect the previous owner pulled this out of another vacuum pump, or changed the motor.
I asked the friend who gifted it to me and he also has no clue whatsoever.

Translation of the photo:
First row: Model
Second row: Current
Third row: Model number
Fourth row: Manufacturing date

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 1:19 pm
by Maciek Szymanski
Today I’ve changed oil in my BL8 rotary vane pump (the description of the vacuum system is in the separate topic: viewtopic.php?f=10&t=13708). I’ve used the cheap industrial grade VG68 class oil for milking machine pumps:

640F0BFC-3FF4-49F3-B815-8148B06F3897.jpeg

On the new oil I’ve reached pressure under 10 microns in the chamber (so probably even less on the pump flange) in 5 minutes. Personally I do not see any reason to use an expensive, laboratory grade oil in the second hand pump if such performance can be achieved without it.

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 1:58 pm
by Mark Rowley
Exactly what I’ve been harping about for ages Maciek. There’s some wild misperception that high grade expensive pump oil is required for the fusor hobby. We’re just not performing anything close to UHV work so it’s not necessary.

MR

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 2:14 pm
by Maciek Szymanski
In fact I won’t be surprised if those expensive oils are the exactly the same product as the mass produced industrial oils just repackaged and rebranded by Kurt Lesker, Varian or Alcatel...

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 4:58 pm
by Cai Arcos
Oops!

I forgot to update this post! I changed the oil and let it run for a 50 minutes or so. Pressure never dropped any more than the previously reported. The oil came filthy once again. I redid the process once again with the exact results.

I have not had time to try once again with more oil, because life has gotten to me (family and university obligations). Furthermore the pump is at the place where my dad works (for triphasic power) so it makes everything more difficult.

To be honest, I have kind of given up on this pump. Two oil changes with no reduction of pressure whatsoever... Even if it is still filthy, a pressure of only around 1 Torr is still pathetic.

Guess I will be looking at some Chicom pumps. My main interest are not fusors, but radiation detectors, and most of the times you are only looking to eliminate oxygen out of the detector so that it's high electron attachment coefficient doesn't screw you over. For that around 50 microns should good enough.

In any case, thanks for all the help.

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 8:04 pm
by Richard Hull
Making GM detectors is a project I have been working on. I will update this effort in the radiation forum as I proceed with my effort. The upshot is that most GM detectors wind up back filled to between 50 and 100 torr with argon or neon and a quench agent. The quench agent is the sticking point. more on this as I go.

Richard Hull

Re: Help me in my baby steps in the vacuum world.

Posted: Sun Feb 28, 2021 11:18 pm
by John Futter
Richard
When we were using Fris grid detectors at work (these are fancy Geiger tubes that position detect) we used Argon and a little 1-2% propane by volume as the quench agent