Help me in my baby steps in the vacuum world.

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Cai Arcos
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Help me in my baby steps in the vacuum world.

Post by Cai Arcos » Fri Feb 05, 2021 3:18 pm

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!
Attachments
WhatsApp Image 2021-02-05 at 16.17.46.jpeg
Set of recommendations
WhatsApp Image 2021-02-05 at 16.01.54.jpeg
Table of recommended oils.
WhatsApp Image 2021-02-05 at 14.43.35.jpeg
Current set-up
WhatsApp Image 2021-02-05 at 16.14.31.jpeg
Original pump 2
WhatsApp Image 2021-02-05 at 16.14.31 (1).jpeg
Original pump 1

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

Post by Richard Hull » Fri Feb 05, 2021 9:46 pm

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
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Cai Arcos
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Real name: Cai Arcos
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Re: Help me in my baby steps in the vacuum world.

Post by Cai Arcos » Sat Feb 06, 2021 8:16 am

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.

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

Post by Maciek Szymanski » Sat Feb 06, 2021 10:15 am

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.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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

Post by Cai Arcos » Sat Feb 06, 2021 6:38 pm

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.

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

Post by John Futter » Sat Feb 06, 2021 6:46 pm

Pump looks like a two stage rotary vane type to me

good find

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

Post by Maciek Szymanski » Sat Feb 06, 2021 10:00 pm

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.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

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

Post by John Futter » Sun Feb 07, 2021 2:59 am

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

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

Post by Cai Arcos » Tue Feb 09, 2021 3:14 pm

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.
Attachments
WhatsApp Image 2021-02-09 at 13.38.12.jpeg

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

Post by Richard Hull » Tue Feb 09, 2021 8:53 pm

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
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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