Vacuum pump

Alberto-sp

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Hello.

I like to make experiments with electricity and that kind of things, so I want to buy a Vaccum pump. I think it´s probably that the final vacuum is sometimes a "lie" like the lumens in the flashlights. Of course good brands like Yellow jacket are reliable.

With a budget about 300$ I can get a Yellow jacket YJ II that gets 20 microns vacuum. The question is, with a 2 stages vaccum pump is it possible to get vacuums bigger that 15-20 microns or not really? To know if it´s worth to expends a little bit more and gett a greatter vacuum.

Thank you
 
What purpose will you put the vacuum pump to?

If you are not evacuating refrigeration systems and holding a deep vacuum for any length of time to remove moisture in the lines you may not need a 2 stage pump, or the ability to pull a very deep vacuum. I used to install hvac systems and had vacuum pumps capable of pulling below 29.9 inches of mercury (500 microns) very handily, capable of boiling off any amount of rainwater than may enter my lines as I was installing a line set in the rain, or capable of purging lines before replacing a compressor.

How much air needs to be removed from whatever system you will vacuum and are you in a hurry. In HVAC trade time is money, so there would be advantage to an 11 cfm capability. If you wanted only to degas resins in a 2 gallon vacuum chamber a small 4 cfm pump is fine.

Give me more info and I'll try to advise you further.

But based on your need to pull a mere 20 microns you can buy the cheapest pump from vevor
 
Thanks for your answer. Is for making experiments with electricity, like CRT, tubes, etc...
 
Thanks for your answer. Is for making experiments with electricity, like CRT, tubes, etc...
A mechanical vacuum pump, at best, will get you down to a low enough pressure to experiment with gas discharge tubes, and things like the Crookes Radiometer. I think home-made plasma globes would be within your reach as well. But in that case you need to be be aware of the danger of implosion when messing around with large evacuated glass vessels.

If you want to experiment with stuff that uses electrons like CRT's, vacuum tubes, x-ray tubes and the like you need a much better vacuum, the kind that can only be obtained with things like diffusion pumps and turbopumps. I've found used & functional diffusion pumps on ebay for as little as $200 but that's a screaming deal that doesn't last long. But you have to be careful, many of the less-expensive ones are missing something, require high power to operate and/or something other (higher) than 110V to operate them. Used turbopumps can be had as well, but you _really_ have to be careful there, many need to be rebuilt or may be damaged. They also need a controller for additional $$. Turbopumps are like small turbine engines but operated in reverse. They spin at up to 100,000 RPMs so one mistake (like inadvertently venting your vacuum system to air while the turbo is running) will likely cause it to blow up. Literally.

Diffusion pumps work on a different principle, using a gas "jet" produced by boiling special organic liquids, to transfer momentum from the jet to gas molecules that wander into the pump, basically urging them on toward the exit side of the pump. The very hot working liquid will react with oxygen in the air so screwing up and dumping your vacuum chamber to air when the diffusion pump is running will cause big problems, too. As a grad student I had the "privilege" of rebuilding a diffusion pump where that had happened, and the parts in the interior of the pump were coated with baked-on varnish. As long as that varnish was in there, there was no hope of getting any kind of decent vacuum out of it. I resorted to using oven cleaner to get it all out, along with lots and lots of other solvents. I got it working again but it was a true PITA to get there. I earned my stipend on that one.

In addition to getting the vacuum pump(s) themselves you will need vacuum fittings and the right kind of tubing. The fittings are pretty special, and so is the tubing. Most plastic tubing outgasses too much to be usable for the high-vacuum side of your diffusion or turbopump. They also will collapse unless they are molded with a steel springlike insert. Stainless steel is the material of choice on the high vacuum side. If you can TIG weld SS you can save some money on fittings: but only if you can do it with ZERO pinholes in the welds.

If you go to the expense of building a high vacuum system for vacuum tubes etc. you also will want to have at least a couple of vacuum gauges. One for the (relatively) higher-pressure side of your diffusion/turbo pump, and another to monitor the low-pressure side of the system.

Sorry to come across as such a Negative Nellie, but experimenting with high vacuum systems can be a challenging and potentially expensive exercise. While there are deals to be had from places like ebay, it takes some experience to figure out what really is a good deal in that field of endeavor. As a high-schooler I had the opportunity to play around with making my own gas discharge tubes and that was fun, and not too challenging. Going past that, well, it gets more difficult in a hurry.
 
My advice with your dollar amount is to get a good HVAC pump. Should be able to find them used, but there is a lot of new ones that are reasonable priced. Then you need vacuum pump oil, and I suggest you get a set of cheap refrigeration gauges. You only need the low side, but when you factor in gauge, hose and add a valve, a cheap Ebay set will suffice. An R12 set will do. The fittings are 1/4 SAE flare. That will get you all sorts of stuff at the hobbyist level. If you are going to need a super precision vacuum, then you need to go as Homebrewed said. Then the gauges and plumbing will get expensive. A $10 low side gauge won't be accurate enough.
My pumps and gauges are Robinair and Four Seaons, But I did auto A/C for a living.
 
My advice with your dollar amount is to get a good HVAC pump. Should be able to find them used, but there is a lot of new ones that are reasonable priced. Then you need vacuum pump oil, and I suggest you get a set of cheap refrigeration gauges. You only need the low side, but when you factor in gauge, hose and add a valve, a cheap Ebay set will suffice. An R12 set will do. The fittings are 1/4 SAE flare. That will get you all sorts of stuff at the hobbyist level. If you are going to need a super precision vacuum, then you need to go as Homebrewed said. Then the gauges and plumbing will get expensive. A $10 low side gauge won't be accurate enough.
My pumps and gauges are Robinair and Four Seaons, But I did auto A/C for a living.
I wish I did auto AC, then maybe I could figure out the proper method how to charge my system when the low pressure lock out has kicked in.
But I barely drive anywhere and I dont live in a sweat box so I can live with it
 
Simply connecting a can of refrigerant to the system overrides the low pressure switch. That is how you get the compressor to kick in after vacuuming the system The unit may short cycle until enough Freon is in the system to stay above the low pressure switch setting. The real trick is getting the correct low, high side pressures at the correct vent output for the ambient temp. That's a mouthful. :)
 
Dudley did a review of the Vevor vacum unit here.
 
The ac guys have proper thermocouple/Pirani gauges available...

Mechanical gauges really just say "I started pumping". And a bit of "dang, I've got a big leak".

If you are doing it once in a while you could use a coil of metal tubing in a cold bath to improve your vacuum some. A cold trap. Bonus points for actual cryo Temps. Liquid N2 would be the right stuff. Dry ice in acetone would work too.

Again, for occasional use you could valve off the higher vac part and either heat Titanium or sputter it.

Sorry, getting to crazy land!

You want a two stage pump. If you don't go to an AC place for a pro pump, consider getting some pump oil and changing it after you get a few hours of run time on your pump. They need to heat up to cook volatiles out of the oil. It's special oil, BTW!

Sent from my SM-G715A using Tapatalk
 
Simply connecting a can of refrigerant to the system overrides the low pressure switch. That is how you get the compressor to kick in after vacuuming the system The unit may short cycle until enough Freon is in the system to stay above the low pressure switch setting. The real trick is getting the correct low, high side pressures at the correct vent output for the ambient temp. That's a mouthful. :)
that did not work for me...
 
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