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Author Topic: vacuum pumps  (Read 239 times)

poisoninthestain

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vacuum pumps
« on: September 03, 2009, 11:03:13 PM »
My homemade vac pump from an old dehumidifer finally died. I'm looking for a new one. Trying to save money. I'd prefer to just buy one. Harbor Freight has some decent crap but 50-75 microns is just too intense a vaccum.

Ideas welcome.
« Last Edit: September 03, 2009, 11:09:48 PM by poisoninthestain »

Vesp

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Re: vacuum pumps
« Reply #1 on: September 03, 2009, 11:16:00 PM »
Aspirator?
Those are easy to get, cheap, and effective. It depends on what it is you are doing though. What is wrong with a really powerful vacuum source?

I have heard you can make a vacuum from an old gas motor, you may want to look into this..
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Formula409

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Re: vacuum pumps
« Reply #2 on: September 04, 2009, 12:13:37 AM »
What is wrong with that! 50-75 microns would be great!
All those pumps have a little spin valve on the side of them that adjusts  how much air is drawn in from the atmosphere so you can knock back the intensity..

I'm using an old medical vac pump pulls down to something crazy, works great and I rarely have to use a heat source because of it....

My glass has imploded because of it but it was due to a hairline fracture in the still head....

poisoninthestain

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Re: vacuum pumps
« Reply #3 on: September 04, 2009, 01:10:46 AM »
Some pumps are loud. My dehumifier pump used to be pretty quiet but used to get intensely hot. Reason it broke is because of some external electrical problem. I think a resistor or something snapped off. Whatever. It wasn't the best pump around but pulling water at ~40C was pretty exciting. All I pretty much did was disassemble the whole thing down to just the compressor, get off the cooling coils and such, and made a few very slight mods.

Aspirators need a nearby sink. Sometimes fitting a coupling on a faucet is a bitch and suckback is sometimes a problem. Probably the worst thing is when the water pressure in your home flucuates. Someone flushing a toilet has happened to me before or taking a bath. With a mechanical pump no worries.

I assume Harbor Freight models carry adjustor valves to reduce the pressure to what you desire even though they aren't exactly meant for laboratory use. I'm probably considering buying one around a ~70 micron range. Sometimes considerably strong vacs around the 30''Hg break the cheaper brands of glass not to mention sometimes the gas won't condense because the condenser isn't cold enough with using just water because the vac is so strong. It happens sometimes. Not a lot, which is good.


I called Harbor Freight to ask about the specs. Everything looks good. I think I'll just stick with one of their models since their prices seem fair.

« Last Edit: September 04, 2009, 01:15:09 AM by poisoninthestain »

wuberton

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Re: vacuum pumps
« Reply #4 on: September 04, 2009, 03:24:59 AM »
I also am looking at Harbor Freight for a decent vacuum pump (http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=98076 ) or something similar... However, regarding the adjustable valve to control vacuum, I stumbled upon this site ( http://www2.swaylocks.com/forums/vacuum-pump-micronshg ) that warns of running it at anything less than full vacuum, which may be a bit much for me, my glassware, and the experiment in general. Please PM me or post a reply letting me know how it works out, as I am getting really tired of endlessly pumping with the hand vacuum pistol-style pumps...

Sedit

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Re: vacuum pumps
« Reply #5 on: September 04, 2009, 04:03:28 AM »
Dehumidifier pump? Can you say more about how this was used as a vacuum source please?
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German

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Re: vacuum pumps
« Reply #6 on: September 04, 2009, 05:25:45 AM »
Aspirator's are nice because they are cheap and easy but man do they use a lot of water. And running those things from midnight to 5am in a motel room sure can be suspicious. Before I got an aspirator I was looking at one of those locking hand pumps (SelectLine I think is the brand) but I wasn't sure how well they work. How about those $75 locking hand pumps? Does anyone use them? If I could get a 40 degree drop in the distill process with one of those things it would definitely be a lot better then an aspirator but I just don't know about them.

Douchermann

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Re: vacuum pumps
« Reply #7 on: September 04, 2009, 05:59:00 AM »
Those hand pumps will require a shitload of pumping.  I got the unfortunate chance to use one for something as mundane as vacuum filtration, and my hand muscles got tired quite quickly.  If you have 75, save up another bit of cash and get a pump from cynmar.  I have one of their lower end pumps, and I tell you, it's a tank.  I've taken it apart about 3 times and cleaned a 3mm deep shelf of rust and sediment from the bottom, and it seems to pull and even stronger vacuum each time.  I'm quite sure the rust is coming from the cast enclosure though, because I took the actual rotary vane section apart once, and there wasn't even the slightest hint of pitting, scratching, or marring.  Eugenol boils at ~120C with my pump, which is all I (and many people on this forum) will ever need.

Goldmember

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Re: vacuum pumps
« Reply #8 on: September 04, 2009, 11:39:21 PM »
Asthma Nebulisor pumps(small diagphram pump)are good for filtrations etc.Cheap too.

poisoninthestain

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Re: vacuum pumps
« Reply #9 on: September 05, 2009, 07:59:36 PM »
Quote from: Sedit on September 04, 2009, 04:03:28 AM
Dehumidifier pump? Can you say more about how this was used as a vacuum source please?


I'm actually quite proud of it since I'm HORRIBLE at anything electrical and I haven't really heard of anyone else ever attempting it for laboratory use. Well, when I started learning about homemade vac pumps I heard about people getting success with modified air conditioning pumps. I didn't have a spare AC but had a few dehumidifiers laying around so I thought wtf I'll give this a shot.

After some days of researching how dehumidifiers work they are easily converted into decent vac pumps. A dehumidifier is essentially a compressor, condenser, and some electrical mumbo jumbo. Most models are more or less identical.

First remove the outer factory manifold which is basically the giant metal shell on the outside of the dehumidifier. After it's gone you'll see the guts of it: the condenser and the compressor.  The compressor is a giant metal heart looking thing and the condenser is kinda like a series of interwoven grates.

Now you have to remove the condenser. Start by following the wires from the compressor out. There should be 3 valves(imagine a heart with arteries) exiting the compressor. One is air intake, one is outtake, and the last is sealed shut(yours might vary). Clip both of them since they're pretty much useless, and the one that starts to merge into the condender just tear out.

You should now have just a compressor with two open valves. Plug the power cord into the wall to test it. It should start pumping. If you put your finger over the one it should suck, and the other should push air out. Attach some vac tubing and you're done.

Also when you're disassembling the condenser expect some loud hissing. Not to worry. It's just freon.

Depending on your dehumidifier source it should pull a decent vacuum. I'd say room temp water at ~30C. They get hot but it doesn't really matter. I've had mine running for hours on end without any problems. It's pretty quite too. Kinda like a hum.

Again, the only reason mine broke is because some internal electricals got torn apart because of improper storage.
« Last Edit: September 05, 2009, 08:02:58 PM by poisoninthestain »

Prepuce1

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Re: vacuum pumps
« Reply #10 on: September 06, 2009, 07:04:17 AM »
If I could add a little to what  Poison said, dehumidifier pumps are almost identical to those in refrigerators. I'm using one now.

When you remove one from a refrigerator or a dehumidifier it's like Poison said. There will be two copper gas tubes leading out of the compressor, and these both must be cut off. The third is already sealed and connected to nothing. You also need to cut off the wiring, but don't remove it from the plug that fits on the compressor or you may have a hard time figuring out what goes where. Make sure you get the capacitor, too, if it has one. Most have them but not all.

One bonus to getting a pump from a dehumidifier is that it will probably have a small fan that blows across the compressor. If you get one of these keep that fan.In fact the one I'm using is still mounted in the dehumidifier frame. That way I can wheel it around if I want to move it.

You have to make sure you maintain enough oil as you use the pump, and if the outlet is at a low level the pump will lose oil, little by little. I now loop a hose about five feet above the pump so any oil leaving will run back in.

Depending on what you use it for, frequent oil changes are important. Water is bad as it causes internal rust; HCl is worse. On the suction side I use two flasks. The first is filled about 1/.2 with water, and the second with oil. This is to catch as much as I can before it goes into the pump.

My first pump lasted about six months before it locked up. The last lived a year or better. I'm hoping the one I have now will go longer, but who knows. I put some pretty strong fumes through it at times.

I wanted to comment also on vacuum causing glassware to implode. Since the highest vacuum you can pull is one atmosphere, is there really going to be much difference in the load on a piece of glassware between a pump that pulls 50 microns compared to one that pulls 70? For the purposes of chemistry there can be a difference, of course, but for glassware it seems to me that there would not. Of course I've been wrong before . . .

PP

akcom

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Re: vacuum pumps
« Reply #11 on: September 07, 2009, 07:06:27 PM »
also keep in mind most of those AC pumps are rated in terms of ultimate vacuum.  That is, what you'll pull right at that little outlet nub.  The ACTUAL vacuum it pulls can vary from there.  I've never managed to pull at 75 micron vacuum with my AC pump on a glassware setup.

edit: As for aspirators, pool pumps my friends!  Have you guys not seen the article on rhodium?  Get a nice pool pump, run it into a five gal bucket full of ice water, throw an aspirator on the output, drain the aspirator back into the backup and viola.  Nice vacuum.  Not to mention you don't have to worry about chemical vapor reacting with oil in the pump like you do with an AC vac pump.
« Last Edit: September 07, 2009, 07:08:40 PM by akcom »

geezmeister

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Re: vacuum pumps
« Reply #12 on: September 08, 2009, 02:58:52 PM »
The Harbor Freight pumps are fine for filtration but are a bit noisy for other uses. I imagine you could devise a box to absorb most of the noise, but there really aren't the sort of thing you want to leave running for hours on end. Great for filtration, no problem hooking a bleeder valve in line to adjust the amount of vacuum-- you will likely need one as without you will have too much vacuum for most filterpaper and will pull holes in it.

The fridge pump / dehumidifier type vacuums tend to die unexpectedly, and most have a long life on them when you acquire them. I've had them that worked without difficulty for as long as two years, and have had them that quit working in a week or two.
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