[kindpastor]

I'm back again with another "would this homemade alternative to pricey labware work" question.  I'm in need of a vacuum pump to accompany a buchner flask, funnel, and filter paper.  I was thinking of just using my ole handi-vac hooked up to a large container that would hold any liquid and keep it from getting sucked up into the vacuum.  Is a vacuum cleaner too strong?  would it break the glass?  I'm just generally worried the thing will be fail.

[Borek]

I would rather expect it to be too weak.

[kindpastor]

Shows how much I know, when I saw a filtration apparatus for sale online it came with a hand pump, so I figured a vacuum cleaner would do the job fine, I guess I'll just break down and buy a hand pump.

[billnotgatez]

http://shopvac.com/vacs/list.asp?hdnSource=index&Browse=6hp

I wonder if ShopVac would work. It is capable of wet and dry so the capture tank is already set.

[kindpastor]

Just so happens I have a shopvac, would it be as powerful as a lab pump?  How is vacuum power measured anyways?

[Borek]

No idea about vacuum power, but when it comes to filtration you just measure pressure. In good lab water pump (however it is called in English) pressure is similar to that of water vapor. That's enough for filtration, for other applications (like vacuum distillation) you may use oil or mercury pump.

I doubt any vacuum cleaner is able to get that low with pressure.

[enahs]

I do not know how much the hand pump cost, however there is another option.
In cars, many of the mechanical components are controlled or timed or tuned by a vacuum system. In order to diagnosis certain problems, you must pull a vacuum and hold it on certain systems and see if there is a leak. It is a hand-held manual pump device with a gauge and they can pull amazing vacuum (just go slow and be careful if you get one, as they are easily damaged, and do not try and pull more then the device is rated for). I mention this to you, because you can by them at many local auto-parts store for relatively cheap, and will even come with hoses that will fit right onto the typical vacuum distillation flask. They might be more expensive then the one you can get from the lab supply shop, no clue.

Also, I suspect a shop-vac would produce plenty of vacuum. They are typically used on a opening of 3+ inches. If you where to make a proper step down without any leaks it will pull a fairly strong vacuum. I have a step down system for my shop-vac for cleaning out the computers, by the old method of putting my finger over it and comparing it to a typical lab-bench vacuum system, they are fairly comparable.

Although, I would much prefer to use a hand pump often then have a shop-vac constantly running while I am doing lab work.

[kindpastor]

Thanks for all the advice, I guess I can try the shop vac before switching over to an auto or laboratory hand pump, whichever is cheaper.

[kelaniz]

I wondered the same thing, and tried several approaches in order to save some cash. One thing I learned, rigged vacuums tend to suck (or not suck, depending on how you interpreted that), you have almost no control beyond the On/Off switch, and when they inevitably fail, it'll be at the worst possible moment. IMO, chemistry can be dangerous enough without the added risk of using a vacuum held together by duct tape and hot glue.

Since a vacuum is such a tricky thing to create and maintain, I eventually decided having consistency, safety and control was worth spending a little cash. Plus, being able to skip all that construction and endless leak patching was a nice bonus.

There's actually some really good hand vacuum pumps out there. The one I've seen the best reviews for is actually for automotive use. It's the Mityvac 04000, although the company has quite a few models. Some are plastic, some metal. Higher end ones can create a good vacuum as well as pressurize.  Best thing about them, they're pretty cheap. The Mityvac Silverline Automotive 04000 seems to be pretty popular. I've seen these for sale from $29-49 USD. The lower end ones that won't keep a vacuum (unless you keep pumping) go for around $10 to $19. Here's some specs on the 04000.

Weight:                3.3 lbs (1.5 kg)
Size:                      12" x 8" x 3 3/8" (305 mm x 205 mm x 85 mm)
Max. Vacuum:       25 in. Hg (85 kPa)
Max. Pressure:     25 psi (172 kPa) 
Displacement:       1 cu. in. (16 cc) per stroke
Gauge Indication: 0 - 30 in. Hg (0 - 100 kPa)

Link: http://www.mityvac.com/pages/products_hvpk.asp.

The hand pumps I've seen from labware suppliers look almost identical to this, except they're  usually plastic, can't pressurize or hold the vacuum, and cost at least twice as much as the Mityvac pumps. I put one of these at the top of my birthday list. 17 days left. I hope I get it

Hope that helps a little. If not, good luck on the shop-vac solution. That'd definitely be fun to try.

-Kel

[Susie]

I'm sorry to *Ignore me, I am impatient* such an old thread.. but this is a topic which I have been thinking about a lot recently, so this thread has been very interesting to me. Has anyone had success with any of these ideas?

I've been thinking recently about trying to make a macgyver style freeze dryer.
My idea is to use a shop vac, a round bottom flask, and an ice-cream-freezer style Ice/NaCl bath, Which I would probably have to insulate very well or keep changing 'cause I'm sure if I did get sublimation, I would get very slow sublimation... Which brings me to a concern about using a shopvac at high pressure for a long period of time: That is probably a bad idea- isn't it? Does anyone have any better ideas about how I might create a low enough pressure for long enough to sublimate some water? Or do you think that the shopvac would actually work?

Thank you so much, chemical forums! I'm sorry I am posting this before I have even introduced myself, but I saw this thread and got excited... I will introduce myself in another thread soon enough. In the meantime though, Hello! Or something like that...

-Susie