I’m considering making a DIY vacuum chamber for preparing sous vide and other silly experiments so I want to buy a vacuum pump. I’ve done a little research but there are a lot of options and I’m hoping some of you can give me some advice. This is your chance to expound on your rarely-sought-after knowledge!
My qualifications for the vacuum pump in order of importance are:
[ul][li]A vacuum of at least 28" mercury*. Higher is even better.[/li][li]Preferably under $100. Used is ok since I won’t be running it all that much.[/li][li]Easy to maintain. Most require lots of oil which I’d like to avoid if possible.[/li][li]Quiet.[/ul][/li]Is there anything else I should be considering? This vacuum pump on ebay looks like what I want but at $30 it seems awfully cheap and I fear that either it won’t work as advertised or it will break down. This used one looks like it might be OK. Thoughts?
BTW, you can get some interesting results if you google “vacuum pumps”.
Can I rant about all the different ways that vacuum pumps are measured? Inches of mercury, pascals, microns…argh! Makes it a pain to compare.
Do you realize that this type is operated by compressed air? It is not electric, you will need a compressor capable of delivering 4.2 cubic feet per minute of air. The pump may be quiet, but the compressor won’t be.
If you’re willing and able to do a bit of engineering (essentially soldering on a fitting, I believe), get a working compressor from an old refrigerator. It will do the job.
In grad school I used a lot of rotarey vane vacuum pumps, and frequently took them partially apart to clean and refill them. We used them as roughing pumps, and got to really low vacuum using a diffusion pump or turbopump afterwards. It sounds as if you need no more than the roughing pump.
That also tels you how the vacuum is measured – unless you’re going to very klow pressures, measuring the vacuum in inches or mm of mercury. A Torr (named after Torricelli) is 1 mm of mercutry pressure, which is an easy conversion. An atmosphere is 760 mm of mercury or 760 torr. A pascal is 1 M/sq. meter, but I never used it in measuring vacuum. Microns measures the pressure in microns of mercury = 1/1000 mm of mercury = 1/1000 torr. Obviously you use this at high vacuum, and you won’t need it for your rough pump.
I did not realize that, thanks. This is why I check with people who know this better than I do.
Hmmm…that’s a good suggestion. I’ll have to look into it–I like the idea of repurposing old parts, especially if it’s cheap. Just so I’m clear, you’re talking about attaching a hose to the air-intake part of the compressor and using that to pull the vacuum, right?
I don’t recommend this.
Old refrigerator compressors are oil-sealed, and will make a real mess if run with an open exhaust port. I speak from experience.
if you use a pump containing oil then you will have to trap all the moisture before it gets to the pump. this is a difficult process outside of a lab or production system.
a pump driven by compressed air has advantages for this purpose. you can bring in the compressed air from another room.
I’m not crystal-clear on the details. There is (originally) no air intake on the refrigerator compressor, it’s a refrigerant intake – the suction side, as opposed to the discharge (exhaust?) side. My understanding is you would install a fitting on the suction pipe to connect to a hose that would go to the piece you’re evacuating, and the discharge pipe would just be open to expel the air from the piece. I don’t know about a mess from that, what I do know is that in the 70’s some automotive shops would use an old refrigerator compressor as a vacuum pump to service air conditioning systems.
I have a Blue Point (from Snap-On) vacuum pump (GA 271-A, shown here – scroll down a bit) that clearly contains oil, and there is no need to worry about moisture. In fact, one of the key reasons to evacuate an automotive A/C system is to remove (boil off) the moisture from the system.
It seems to me that you and beowulff are familiar with vacuum pumps that operate differently from the ones I’ve used in servicing automobile A/C. I’ve never had to be concerned with moisture or making a mess.
ETA: It is offically recommended to change the pump oil occasionally, but I’ve been using that thing for close to 15 years, never changed the oil, and it still works perfectly.
if you got a working refrigerator or freezer that you would want to try to use (not saying it would work for long, those do die if run without the oil not being in the compressor) then it would be good to get the refrigerant reclaimed at a shop before opening the system.
I’m not a vacuum expert, but I do have some experience.
There are quite a number of different pump designs, and each design type as many variations.
Good-old-fashioned roughing pumps were completely submerged in oil. These made a “burbling” noise as they pumped, and you could get a pretty good idea of the vacuum just by listening. Refrigerator pumps were most often piston or wobble-plate pumps. They are oil-lubricated, but they don’t have a reservoir - they rely on the closed system to circulate the oil. These pumps tend to disperse oil in a very fine mist if you run them “open.” They also require oil to lubricate and seal, so if you do run them open, they need to have oil added periodically. There were some old Frigidare(?) pumps that used carbon vanes, and they were oil-less, and would be perfect.
Modern pumps can be oil-immersion or any one of a number of oil-free designs, including wobble-plate, Teflon vanes, diaphragm, etc.
If you are only going to be pulling an occasional vacuum, I’d get something like this:
I have a nice wobble-plate pump I bought on ebay, but I think it’s overkill for what you need.
It’s possible that the ones I was referring to were like this. It’s been about 30 years since I’ve seen one, so I don’t remember.
This is something I’m familiar with, as these are used in auto repair to test devices operated by engine vacuum. I would say the criterion isn’t occasional use, but rather the volume of space to be evacuated. Mine will just pull 28". It’s fine for a volume of a few cubic inches, but would be tedious for a cubic foot. Unlike the pumps we have so far been discussing, which will generate continuous vacuum, this type will realistically only apply a static vacuum – you just can’t squeeze it fast enough to compensate for any leakage. In some applications, the fact that it ties up the use of one hand may be significant.
It occurs to me that I don’t know what the requirements are for sous vide applications. The electric pumps may be overkill. I gather that it’s a matter of evacuating a bag and sealing it thus; the sealing process (quickly enough to preserve the vacuum) may be much more of a challenge than the evacuation.
To quote Raiders of the Lost Ark: Obviously, we’ve come to the right men. I really appreciate all the help.
There’s an appliance store right down the street from me so I might check with them on reclaiming a compressor. I’ve done some digging around and as beowulff noted they can spray oil. I’ve seen a few suggestions on line on how to trap (or filter) the oil. I still like this route but it’s becoming more complicated.
In case anybody’s interested here are a couple of links I found:
I would totally go for that except that I expect to evacuate at least a cubic foot of air and I assume it would take forever with that.
High-quality sous vide vacuum chambers can pull 28-29" of mercury so I’d like to at least match that. I hear one can do interesting things to food if one can pull 29+" mercury so that’s what I’m shooting for. It’ll also be fun to boil liquids at low temperature. I intend to start by bagging the food in the Food Saver bags that have valve on them and dropping them into the chamber. Some day I may get more ambitious and come up with a way to heat-seal bags.
I don’t mind experimenting if it’s not expensive, which is why the reclaimed compressor sounds inviting.
The FoodSaver heat seals the ends shut already, you won’t need any extra equipment if you already have that. But if you want, we use one of these at work for heat sealing bags. When used with heavy (food safe) bags, the seal stands up to being boiled for hours upon hours without letting loose. We seal gallons of hot soup in them, toss them in ice water to chill them, freeze them and then when we’re ready to heat them toss the whole frozen bag in boiling water until it’s back up to temp.
Let me add one word of caution: Vacuums can be dangerous.
Never evacuate a glass or plastic chamber (I wouldn’t even trust a bell jar without a screen around it). Metal containers can buckle unexpectedly, pinching fingers. A 1’x’1’ area will have nearly one ton of pressure on it at full vacuum.
Yeah, that’s good advice that I need to keep in mind. It’s easy to forget how much pressure can build up on the outside. I’m planning on copying this guy’s design: http://www.housatonicrr.com/VacChamber.htm
Does that look sturdy enough to you? If I make it with 8" PVC pipe about 10" tall it’ll be around 1.7 sq/ft in surface area, volume of ~0.25 cubic feet.
Here’s a good demonstration, albeit on a larger scale of how fast that can happen. You can see where fingers could get pinched if someone was handling that (and heat wasn’t involved). After watching this version I always get nervous when I see the other versions where they use gloves and roll it around in a small pool of water by hand. Those walls can stand up to a lot of negative pressure. I assume there’s some techy word that means something similar to “super heated” where it just takes one little thing to set the whole thing off.
An aspirator pump is a very simple solution. They use a continuous supply of water under normal house plumbing pressure to pull a vacuum by the venturi effect. In principle, they can pull a vacuum equal to the vapor pressure of water ~30 mbar. As a kid I used one of these to boil luke warm water. These are dirt cheap and use no oil. The disadvantage is that you are wasting water the entire time you are pumping, so are best for a situation in which you want to pump something down and seal it. If what you are pumping contains water, you aren’t getting lower than the vapor pressure anyway. I have one of these with a garden hose fitting on the suction side and a kitchen sink fitting on the water supply. I purchased it from a pet shop for doing aquarium water changes.
I really appreciate all the help.