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smaerd
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[*] posted on 4-9-2010 at 11:01
Help with Water Aspirator Design


So I've been weighing the pro's and con's of a lot of vacuum sources, and I think an aspirator is all that I need and well with-in my price range. I've read through all the threads I could find on here about them and did some research via google. I'm pretty new to the whole concepts of pressure and the physics behind it all(Venturi effect is really cool though!).

Anyhow I do have some question's/concerns that I think only sci-mad could help me to find answers for. I'm not looking necessarily for answers just where to look to find them.

Anyways here's what I'm thinking for the aspirator($15):
Quote:
It has a maximum free-air pumping capacity of 11.5 liters per minute at a water-flow rate of 6.5 liters per minute.

http://wardsci.com/product.asp_Q_pn_E_IG0005450_A_name_E_Pol...
I decided PP would be the best for corrosion issues, but I don't do anything too crazy anyways. My main concern is, if I am running a Water Pump that is going at say 3000gallons/hour or 50gallons/minute is if it is going to have any deleterious effect on the aspirators functionality? From what my limited research has concluded, is that no matter what the vacuum is limited by the water's properties not so much by how much water is flowing through it(at least at a certain point).

The water pump I chose is this($50)-
http://www.harborfreight.com/1-hp-3000-gph-dirty-water-subme...

The main reasons for this are because of the price, the fact it's not made out of cast iron(rust issues), it has a heat shut off function built in(hot water also effects the vacuum), it can accept small particles just in-case something did get caught in the system it wouldn't blow up, and it appears by looking at the product assembly that it would be very very easy to apply fittings to it for plumbing.
http://manuals.harborfreight.com/manuals/93000-93999/93819.p...
See page 13 and part #34 to see what I am referring too. A nice threaded tube :).

It runs at 750 watts they say which will end up probably costing me 10 cents in electricity a year assuming I use it a ridiculous amount.

For the basin or water container, I am thinking about a 20gallon plastic trash can($10).

I figure the plumbing will cost $10-$20 dollars. This is where I am stuck though(sorry for the length of this post already)! In one of the other threads where a member explained their set-up: http://www.sciencemadness.org/talk/viewthread.php?tid=13241#...
Quote:
Originally posted by Poppystraw
[img]http://www.sciencemadness.org/talk/files.php?pid=169516&aid=9475[/img]

- I noticed they had a valve on the water in-let. Obviously this is to control the flow of water running to the aspirator, but I guess my concern is how necessary is this? Could it strain the pump?
- What is with the one tube leading to the water aspirator and then it looks like there is another tube leading back into the water resevoir, what does this do? Is that in case there is too much water running through at once?

Thanks for any help, or ideas.

[Edited on 4-9-2010 by smaerd]

[Edited on 4-9-2010 by smaerd]
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[*] posted on 4-9-2010 at 11:07


My main problem with the recirculating aspirator pumps is that the pump heats up the water very quickly reducing your maximum vacuum. You will need to have some external way to cool the water to get a good steady vacuum.
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smaerd
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[*] posted on 4-9-2010 at 11:31


My basement is always at a relatively cool temperature which means after each use the water will be able to cool down. I can see the cause for concern though...hmm.. For my condenser reservoir I usually just throw in a couple cups full of ice, I'd imagine doing the same would work(?), and snow when it is winter.
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watson.fawkes
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[*] posted on 4-9-2010 at 12:50


Quote: Originally posted by smaerd  
The water pump I chose is this($50)-
http://www.harborfreight.com/1-hp-3000-gph-dirty-water-subme...

The main reasons for this are because of the price, the fact it's not made out of cast iron(rust issues), it has a heat shut off function built in(hot water also effects the vacuum), it can accept small particles just in-case something did get caught in the system it wouldn't blow up, and it appears by looking at the product assembly that it would be very very easy to apply fittings to it for plumbing.
You need about 100 gallons/hour. You've specified a pump at 3400 gallons/hour. That's total overkill, which is a problem for your goal. At that rate difference, you're more-or-less running the pump into a closed outlet. All that kinetic energy has to dissipate as heat. That's just like putting an extra heater into your pumping loop. One of the larger HF "mini submersible" pumps or one of their fountain pumps should do you just fine. Overspec the flow rate a bit (but not by a factor of 34), as you'll have lower flow rates than their maximum from the static pressure drop in the aspirator.
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smaerd
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[*] posted on 4-9-2010 at 13:25


Thanks so much watson.fawkes!

Pretty much that fixes my whole design to be even more cost friendly and less spacious. I use a 130gph submersible pump for my condenser rig. Maybe I could even have these two sharing the same water reservoir.

so I'm looking at the 145 gph model but I don't think it will pull enough water because the reservoir is about 2 feet deep and as the height goes up the flow goes down(which I know you know). Also the ID out-let for the 130gph mini-pump I have is quite small, probably not enough to really increase the volume of the tubing through adapters and still maintain a 130gph(or in this case 145gph).

So I think the most reasonable mini-pump would probably be the 258gph model? But that might even be over-kill...hmmm... I'll have to figure out how to expand the ID so it will fit an aspirator as well, but maybe what I could do is just fix some poly-ethylene tubing on the out-let nipple, then find some sort of fitting to expand from the same ID as the tubing to the desired size(I think 3/4in) for the aspirator. Hmmm..

I'll think about this, I really appreciate your input, I just saw that post(linked to in my first post here) and the pump in the picture was quite massive and I wasn't sure exactly why. Ignorantly I thought I should follow suit even though I knew full and well I only needed about 30psi.
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[*] posted on 4-9-2010 at 14:02
hot air


You could generate a moderate vacuum of 40-100torr using compressed air and a pneumatic venturi vacuum generator. Compare the water aspirator at 22 torr.

They are rugged, require an air flow around 4 scfm @ 70psi for best vacuum. A 2-3 hp 'oil' compressor seems a good place to start -- big enough, not too large nor expensive.

You would need to vent the exhaust air.

Vaccon makes the venturi devices, so do many others.
http://www.vaccon.com/J-Series-M-home.aspx

I use a very small one in my desoldering rework station and can vouch that it does not fail to suck.
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[*] posted on 4-9-2010 at 14:46


Atmospheric pressure is 1013.5mbar, a dyson drops that to 700mbar (30% of the atmosphere gone), I can suck to 200mbar with my mouth (80% gone, ladies..... :P), the numbers in the post one up for the venturi are 133mBar to 53mBar (87 - 95% gone), a water aspirator can manage ~20mbar theoretical (~98% gone), my fridge pump is running at around 15 - 10mbar (99% gone).

Glass aspirators smash, metal ones corrode, plastic all the way.

Have the pump outside the tank and throw ice into the water. Watch out for bubbles flowing back into the water suction line (that will fuck up the stability, a lot).

You need pressure for the aspirator to work, as you're blowing the water through a small orifice at speed; the speed defines the vacuum level it can achieve. Many high volume pumps, be they for solids, liquid or gases, can't pump at both high volumes and high pressures. Garden fountain pumps tend towards high flow rates over pressure.

The normal water mains runs at about 3bar here, ~30psi. So your pump needs to maintain the flow rate Watson suggested somewhere around that pressure.

With respect to the garden fountain pump, 3Bar is enough to push water to the top of my house, about 30m up. A garden pump usually only deals with a metre or three.

Drastically increasing the water pressure doesn't help, the maximum vacuum is limited by the vapour pressure of the thing going through the aspirator. Water in your case.

The vapour pressure changes with temperature. At 20C, it'll start dying around 50mBar. At 0C, that's 20mBar. The coldest I can keep my condenser with ice is about 4C, with a tiny fountain pump in it.

I have finally discovered how to render and upload videos to youtoob. I have a ~30 minute one in which I pull a few fridge pumps to bits and talk about nomographs and things. You might like to see that. I will upload it soon.

[Edited on 5-9-2010 by peach]




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[*] posted on 4-9-2010 at 15:08


Quote: Originally posted by smaerd  
So I think the most reasonable mini-pump would probably be the 258gph model? But that might even be over-kill...hmmm...
You've got two parameters here: pressure and flow rate. You need adequate flow rate at some minimum pressure. The pump you had was obviously overrated; the smaller HF ones are not obviously the right ones. Just like blowers and their fan curves, where air is the fluid, pumps have pressure vs. flow rate curves. You want a pump that's adequate, but not too much. The little HF submersibles might work, but they also might not be capable of adequate pressure and flow. If you see a flow rate listed by itself, it's just a maximum flow without any static pressure drop (either from height or friction). So the 258 gph one might be adequate, since it's not going to pump that much with an aspirator on the line. HF sells another pump you might look at; it's a marine bilge pump with a stainless steel body and 12 V DC motor. That one might develop more pressure. You'll have to experiment unless you can find pump curves for these. I suggested the tiny ones because they're cheap and might work for you, even if they don't develop quite as much suction as a larger pump will; you can upgrade as you need to.
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[*] posted on 4-9-2010 at 15:12


Quote: Originally posted by peach  

Glass aspirators smash, metal ones corrode, plastic all the way.
In my short 45 years experience with many different aspirators of all three flavors, glass aspirators pull the best vacuum, use less water, and are quite indestructable. Wrap those suckers with good plastic tape and quit driving your lorry over them. I bought two glass aspirators about 30 years ago and still have both of them. A prof once wisely stated "learning not to smash glassware is an essential part of the training of a chemist".
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biggrin.gif posted on 4-9-2010 at 15:29


Quote: Originally posted by peach  
Atmospheric pressure is 1013.5mbar, a dyson drops that to 700mbar (30% of the atmosphere gone), I can suck to 200mbar with my mouth (80% gone, ladies..... :P),
True, we all suck to varying degrees :D, but I think you conflate the limiting vacuum at zero flow with vacuum at a useful flow. I believe that a lot of useful work can happen at 100 torr (=130 mBar = -26" Hg) @ 1scfm (~28 litres/minute)

The pneumatic venturi vac has virtues of simplicity and no moving parts and will reach into the single digit torr values at no flow, too.

They are so simple you could make one with three different drill bits and a block of your favorite plastic.

If you are doing solvent reduction instead of solid separations, the fumes vent from the exhaust, while with a water aspirator, solvent fumes aggregate in the reservoir.

My point is that waste vapor disposal may also dictate the vacuum source.

Personally, I would prefer that, while preparing 1-4 carbon linear alkyl mercaptans, the exhaust vents into the Republican National Committee, but forgive the digression.
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[*] posted on 4-9-2010 at 15:34


I feel that I should stick up for metal aspirators. I've used one for ~5 years without a problem. So, as with any material selection, it all depends on your intended usage. Mine is chrome plated brass, costing about $15.



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[*] posted on 4-9-2010 at 15:41


Quote: Originally posted by Magpie  
I feel that I should stick up for metal aspirators. I've used one for ~5 years without a problem. So, as with any material selection, it all depends on your intended usage. Mine is chrome plated brass, costing about $15.
I agree Magpie. There is nothing wrong with them. They were standard before they were displaced by the plastic thingies.

But if you compare them to the glass models, the glass ones produce a harder vacuum with less water flow. I have several of all kinds, and I keep comparing them, especially in summer when the water is not as cold, and I keep coming back the old glass ones.
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[*] posted on 4-9-2010 at 16:51


@Peach - thanks so much for sharing all that information. A video sounds awesome! I believe youtube limits videos to 10 minutes so you might have to do 3 parts :).

@Watson.Fawkes - I'm quickly learning here. GPM/GPH have no real correlation to PSI, which makes sense now that I've seen it. Most of those submersibles do have really low PSI though just as peach said. Your right though this is going to take some experimentation, but I think I'm going to do some more research on some pumps.

http://www.iprocessmart.com/techsmart/formulas.htm
I found a formula for estimated PSI for water pumps which can save me some trouble!

Quote:

HP =
Where

GPM = Gallons per Minute
Head = Height of Water (ft)
Efficiency of Pump = %/100
PSI = Pounds per Inch

Specific Gravity of Water = 1.0
1 CuFt per Sec. = 448 GPM
1 PSI = A Head of 2.309 ft (water weight)
62.36 lbs per CuFt at 62°F


This helps me better understand the equations involved here. Once I find a better pump candidate I'll report back :D. It really is misleading though that the Ward scientific site says that 7.5psi is adequate, because I'm sure if I ran 7.5psi through that thing it wouldn't be pulling 28.5"Hg...
edit -
http://www.harborfreight.com/1-inch-clear-water-pump-1479.ht...
According to the calculations above if this pump was running at 100% efficiency it would have approximately 79.08psi, possibly more because I'd be shrinking the outlet size from 1" to 3/4"(I think), which would surely suffice and means that if it were running at 40% efficiency it would still push approximately 31.54psi. However it's cast iron and all the reviews mention the impeller blades rusting... Ahhh, maybe there's a still a better candidate :)

http://www.harborfreight.com/3-4-quarter-hp-1-inch-shallow-w...
This one can go from 20-50psi, but 900gph is pretty intense and unnecessary..

@entropy51 - I totally agree with you about learning how to not smash glass, but I can't really afford to replace glass(could impede my experimentation for months), and I am a total novice :).

@Magpie - that's good to be mindful of. Maybe I will go for a metal one, but right now this pump is the most important factor :)

{edit}@Anyone - What kind of regulators/meters would I need to figure out the PSI running through a water system or would it be the same as an air system? I'll just google that :P

[Edited on 5-9-2010 by smaerd]

[Edited on 5-9-2010 by smaerd]

[Edited on 5-9-2010 by smaerd]
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[*] posted on 4-9-2010 at 17:14


Here's a PDF I just made with some information in it... same file, three times, no idea how mediafire works on here. Keep in mind, it's 2am here and I'm about to go to bed. I'll add some solvent curves tomorrow maybe.

http://www.mediafire.com/file/19r3lv38ho4ylva/vac%20pump%20c...

http://www.mediafire.com/?19r3lv38ho4ylva

{edit} before editing... I realize the-tube is now limiting to 10 minutes. I bet entropy loves that. :D I don't, because it takes for fk'ing ever to edit videos, never mind on a 256mb computer, and I absolutely hate doing it. Video editing is for arts students (you know maths is an art subject? Hmmmmm, odd exception). So it will need to be in sections, until youtube give me an 'annoy entropy' account.

Quote:
If you see a flow rate listed by itself, it's just a maximum flow without any static pressure drop (either from height or friction).


Indeed, the flow rates are pretty much ubiquitously under the best possible circumstances; nothing blocking the outlet, no pressure head. And the pressures may assume 0 for the flow rate, as the static pressure. To 'show off' the numbers.

In the UK, every hippy went caravan mental in the 60's and 70's. There are pumps specific for dropping into a sump in the caravan to supply the taps inside. I expect they probably produce flow rates and pressures similar to the normal mains.

Although, I've never had the misfortune to live in a caravan, so I'm not entirely sure. But my hippy'esque instincts tell me, it's likely close. I suppose the US equivalent is a trailer.

"The J is like an H in that case ricky...." "whatever...."

Quote:
In my short 45 years experience with many different aspirators of all three flavors, glass aspirators pull the best vacuum, use less water, and are quite indestructable


You're getting kind of old entropy, are you sure they're not clear plastic? Or that you're using them on regular basis and not just developing dementia? Yeah, feel the age related jokes in return.... :P :D ;)

I get your point, but glass is far from indestructible.

Yes, I do love seeing glass aspirators and diffusion pumps. Very pretty. But it takes time to develop that sensitive touch the girls and glassware enjoy. Which I suspect an old salt like you has, but a lot of people here (including myself) are still working on it. You can't recommend glass over plastic to someone who's starting out. It'll be broken the first time they use it.

And when you say harder, by how much? If it's within the important range, the cost and break-ability take over.

I always thought practical chemistry was something girls would be better at, with their gentle nature.

Quote:
True, we all suck to varying degrees :D, but I think you conflate the limiting vacuum at zero flow with vacuum at a useful flow. I believe that a lot of useful work can happen at 100 torr (=130 mBar = -26" Hg) @ 1scfm (~28 litres/minute)


You're correct. In fact, that's something I strongly suggest in the video, that using rotary lab pumps and such is usually the opposite of smart; as the BP rockets below zero, the pump drains your bank account, it's very heavy, uses up loads of desk space, it's very noisy, it smokes the room out with oil mist, the trap drains the account more and the cryogenics drain it a bit further, for no reason.

I aim for 100mbar -> 10mbar for distillations and whatnot.

The only major benefit from aiming for 50 -> 1mBar is breaking azeotropes. Chemistry agrees with you and I, the diaphragm pumps usually only manage 100mBar or so.

Quote:
The pneumatic venturi vac has virtues of simplicity and no moving parts and will reach into the single digit torr values at no flow, too.


But I disagree about the air based venturi's. Air compressors and the tools attached to them are eye poppingly inefficient. A $20 wall socket drill from the hardware store takes something like 6-8HP to power from a compressor for the same tool performance. Shiiiiiiiiiiiiiiiiiit! :o That's A LOT. Orders of magnitude out of line. The governments agree with me, as high pressure tools and spraying are now being phased out (yes... high pressure spraying is better for fine finishes ;) I've spoken to a Sata representative who confirmed that).

Even cheap compressors of that kind aren't that cheap. And they produce a gigantic amount of noise. I have to shout over them during the day. At night, it'll take about 30 minutes before the police turn up, telling me to shut the fuck up.

When you can get ten times lower (and bleed air in to reduce the vacuum) with a free, virtually silent, fridge compressor.

Quote:
Personally, I would prefer that, while preparing 1-4 carbon linear alkyl mercaptans, the exhaust vents into the Republican National Committee, but forgive the digression.


Nought-tay boy! :P

Quote:
I feel that I should stick up for metal aspirators. I've used one for ~5 years without a problem. So, as with any material selection, it all depends on your intended usage. Mine is chrome plated brass, costing about $15.


Quote:
I agree Magpie. There is nothing wrong with them. They were standard before they were displaced by the plastic thingies.

But if you compare them to the glass models, the glass ones produce a harder vacuum with less water flow. I have several of all kinds, and I keep comparing them, especially in summer when the water is not as cold, and I keep coming back the old glass ones.


I disagree with both of you. Use a free fridge pump. As you may have seen in the AlCl3 threads, my brand new chrome tap is now turning green in the presence of tiny amounts of hydrogen chloride.

It does depend on what you're working with when talking about materials. Essentially, if you're expecting acid gases, you want plastic or wash bottles and a fridge pump (or no washes and disposable pumps).

Just about every metal you can easily buy is going to corrode around one acid gas or another. Monel is the only way out, and it's ten times more expensive than normal steels, like 316; literally.

[Edited on 5-9-2010 by peach]




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[*] posted on 4-9-2010 at 18:20


Quote: Originally posted by peach  

You're correct. In fact, that's something I strongly suggest in the video, that using rotary lab pumps and such is usually the opposite of smart; as the BP rockets below zero, the pump drains your bank account, it's very heavy, uses up loads of desk space, it's very noisy, it smokes the room out with oil mist, the trap drains the account more and the cryogenics drain it a bit further, for no reason.

I aim for 100mbar -> 10mbar for distillations and whatnot.
...
But I disagree about the air based venturi's. Air compressors and the tools attached to them are eye poppingly inefficient. A $20 wall socket drill from the hardware store takes something like 6-8HP to power from a compressor.
It occurs to me that I may have misunderstood the intent of the water aspirator vacuum.<br /><br /> I always used (past tense!) them for filtration or solvent stripping, and it didn't occur to me that someone might want it for distillation, normally the province of the insufficiently-accursed oily, smoky Welch 1402 two-stage rotary vane pump.<br />
Generating a vacuum is much less ambitious than running a pneumatic impact hammer. For a vacuum venturi, most 2-3 hp compressors meet the necessary flow handily -- that's about $200 US.<br />
For mini and micro preparations, 1.5hp and 3scfm@70psi may be a serviceable $100 minimum. Shove it in a cheap steamer trunk and put a better baffle on the air intake for effective noise abatement<br />
I am very interested in the mass flow you can get from a refrigerator compressor. They are compact, quiet, ubiquitous, and probably not expensive even as a new replacement component.
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[*] posted on 4-9-2010 at 18:44


Nice pdf peach. You seem to be in the know about vacuums and all that. Have you ever thought about using maybe a cheap Air Compressor, an Air Flow Regulator, and maybe a compressed air venturi?

Even the cheap car air compressors seem to be going at like 100+PSI. I'm not sure how to go about modding one or an air compressor in general but right now it's looking like a viable option.

If only there were cheap refridgerator air compressors commonly available. Maybe I need to refine my search a bit more but they seem to be in the $200 range, and at that rate I might as well go buy a rotary vane pump...
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[*] posted on 4-9-2010 at 20:29


Getting the right pump for any application is just like getting the right fan for a hood. A pump will have a curve of head vs flow (ft vs gpm). This is called the "pump curve." You need a pump that can provide the correct gpm at the pressure drop of your aspirator.

My household water pressure is something like 60 psi and drives my aspirator very well. I don't know its water consumption as I've never measured it.

If, for example, a typical aspirator requires 2 gallons/minute at 30 psi, then you need to find a pump that can deliver that flow rate at that pressure. The pump curve (available with the pump or from the manufacturer) will tell you if that is possible.

The formula you presented is not in the form of an equation so I was not sure what it was. It possibly gives the power requirement, but I didn't investigate.

Pressure is sometimes stated in psi and sometimes in feet of water. The conversion is 1 psi = 2.31 ft.

[Edited on 5-9-2010 by Magpie]

[Edited on 5-9-2010 by Magpie]




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[*] posted on 5-9-2010 at 04:06


I bought a plastic aspirator pump, but never used it as I also had to buy the pump and piping for the water flow. Then I found a fridge compressor for £5 (USD 8 ish!) so I never bothered with the aspirator. Ebay will usually find me a new fridge pump for £25 and a local search of fridge breakers will always find me one for well less than that used. I may never bother with the aspirator, I'm on metered water so I pay for tap use, so a full pump recirculate unit is a necessary cost.

At £5 a pump I may not even bother with expensive scrubbers!
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[*] posted on 5-9-2010 at 04:24


Quote:
It occurs to me that I may have misunderstood the intent of the water aspirator vacuum.

I always used (past tense!) them for filtration or solvent stripping, and it didn't occur to me that someone might want it for distillation, normally the province of the insufficiently-accursed oily, smoky Welch 1402 two-stage rotary vane pump.


The idea is used for all kinds of things. Industrially, they still use them and blow steam through them (maybe entropy could give that a go with his glass one and his wife's steam cleaner, "It's for the good of science!"). Or magpie with the metal one.

A diffusion pump is effectively an aspirator, good down to around ^-10mBar. Note the to the power of sign and polarity, that's not 10mBar.

Quote:
Generating a vacuum is much less ambitious than running a pneumatic impact hammer. For a vacuum venturi, most 2-3 hp compressors meet the necessary flow handily -- that's about $200 US.


That is a massive chunk of money to be spending on something so noisy, that generates a relatively poor vacuum and that wastes so much energy as heat.

A fridge pump is free, produces a stronger vacuum, is all but silent, it's all done for you in a nice, welded, tiny can you can move around and I can now get them out and wired up again in roughly 3 minutes with a screwdriver, pair of pliers and wrench; a girls kitchen drawer toolkit.

If you already have the pump, or are getting into spraying, it's 100% fine. But not really if the goal is only to produce a vacuum.

Quote:
I am very interested in the mass flow you can get from a refrigerator compressor.


It's small, very small; almost as small as my penis, on a cold day. I might measure it (the flow rate) today and add it to the video prior to posting it.

But flow rate doesn't matter for distillations. Even the tiny CFM of a fridge pump is enough to easily deal with taper leaks and condenser inefficiencies.

The low CFM actually helps, because it's impossible to apply the vacuum violently if going from flicking the power on. The solutions have more of a chance to degass rather than bump over. Buchi now sells a controller to do this. Something the fridge pumps do inherently and that Buchi probably want $1k for.

The Buchi pumps also work at around the fridge pump pressures, a little higher actually I think.

There you go, thousands for something in a nice box with their logo on it that does exactly the same thing, worse, as something free from the dump (genuinely recycled back into use with little extra input).

A fair amount of lab supplier gear is shockingly overpriced. Truly. Because they have a captive audience with a lot of money and not many other options.

Quote:
Have you ever thought about using maybe a cheap Air Compressor, an Air Flow Regulator, and maybe a compressed air venturi?


I did, for about two seconds, then put the idea in the bin. See the above issues.

Quote:
I bought a plastic aspirator pump, but never used it as I also had to buy the pump and piping for the water flow. Then I found a fridge compressor for £5 (USD 8 ish!) so I never bothered with the aspirator. Ebay will usually find me a new fridge pump for £25 and a local search of fridge breakers will always find me one for well less than that used. I may never bother with the aspirator, I'm on metered water so I pay for tap use, so a full pump recirculate unit is a necessary cost.

At £5 a pump I may not even bother with expensive scrubbers!


Important statements here.

[Edited on 5-9-2010 by peach]




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smaerd
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[*] posted on 5-9-2010 at 08:09


@Magpie - Sorry I forgot to include what that equation was solving for. It was for Horsepower I fixed the above equation, I thought the image I copied the location of had it included my apologies.

@Peach - you keep referring to refrigerator air compressors and them being free... Yet on the worlds favorite auction site they are $60+ used, $200-$300 new. It's not like I know people who throw away refrigerators frequently, and I don't think they allow civilians to access scrap yards(at least where I live). In all of my life I've never seen a refrigerator out at the street for the garbage collectors. So whats the secret, how are you getting these for free?

I think I'm just going to save up for a cheap/used rotary vane pump. It may be 150% the cost of an enclosed system water aspirator or fridge air compressor, assuming I could assemble/acquire either of these to working standards, but it sounds like a lot less of a hassle.
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peach
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[*] posted on 5-9-2010 at 17:49


VISIT THIS THREAD!

Go to the local tip and take one, ask for one, buy one from the guys there with a few beers, joints, £5 note, a funny joke or your natural charm, or wait for a friend to throw one as they upgrade the kitchen.

If $300 is the best you can manage, you're not even trying.

[Edited on 6-9-2010 by peach]




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[*] posted on 5-9-2010 at 23:13


Well the fridge pump I have cost me £5 whatever that is in your currency, it's almost free. It came with oil inside and the vendor fitted a lead and power plug for that price. It's slow but it works as pressure or vacuum so I'm happy.

Go head for a kitchen appliance recycling store in a down market suburb. They spend their days making old fridges and washing machines work with spares salvaged from like machines. They usually have several spares in stock so can sell you pumps for silly cheap money.

Locally if a builder is doing a kitchen refit then possibly one thing doesn't work so the house gets a new kitchen and the local breakers get the parts for salvage or resale.
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[*] posted on 6-9-2010 at 08:10


Quote: Originally posted by Contrabasso  

Locally if a builder is doing a kitchen refit then possibly one thing doesn't work so the house gets a new kitchen and the local breakers get the parts for salvage or resale.


That's a great idea!




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