Sciencemadness Discussion Board

good pump?

mnick12 - 1-8-2010 at 17:26

So I was looking around in our boat house yesterday, and I found an old vacuum pump. It works fine but needs to some tlc, I have sanded off the rust and tomorrow I am going to re-paint it and replace its power cord. The thing weighs close to 25lbs and looks like all the pumps I have seen. On the label it says "JB fastvac 3cfm-2 stage 85L a minute."

I know really nothing about vacuum pumps and what qualifies as a good pump. So my question is, is this a good pump? And how good of a vacuum could this pull?

One other thing,
what kind of things do people use vacuum pumps outside of a lab for? The only thing I have heard of is removing water from AC lines, but we dont have AC up here.

Any help would be appreciated.
thanks, mnick12.

P.S- forgot this: http://www.jbind.com/tools/UserFiles/Image/inst-eliminator.p... . My pump is a much older verson of this one.

Oxydro - 1-8-2010 at 17:33

Fiberglass work (vacuumbagging) is the only reason I can think of it being in a boathouse. Just a guess.

peach - 2-8-2010 at 10:24

Sorry to be a gimp but... if you can't answer this yourself you probably don't really know what you're doing.

But everyone has to start somewhere and yes, HVAC and vacuum bagging pumps will work fine for distillations and 3CFM is easily enough for glassware from B14 to B24 and up to a few litres of volume.

I've owned 10CFM 0.01mbar pumps that cost thousands new. They're designed for industrial use, degassing resins, evacuating large chambers and smaller ones very quickly. When degassing, the pressure has to be low and there will be A LOT of foaming and gas coming through the pump it's self (gas dissolved in the epoxy / polyester resin before and during mixing), so they need to have low pressures and high CFM to prevent bubble voids in the finished, cured product; which weaken it in the same way that foamy chocolate is easier to snap than solid, dark chocolate.

My favourite pump of all is a tiny 1.3CFM I can easily pick up and move around. It'll easily evacuate the glassware in under a minute.

I'll spend hours or days working on something, so a minute or two to pump down is nothing; and I can get on with other tasks as it goes. Often, connecting the 1.3CFM pump directly to the glass will cause the liquids to violently bump, and I have to purposefully apply the vacuum slowly. They'll even do it with fridge compressors, which has pathetically tiny CFMs.

A large number of solvents begin boiling at room temperature below 100mbar; 1/10th of an atmosphere. To put that into perspective, an aspirator and fridge pump (free) will manage around 35 mbar. A rotary will usually do tenths of a mbar. Which is deep enough that it actually becomes a problem when distilling things, as the boiling points of the solvents drop so low they won't condense at 0C and need sub-zero traps to capture.

The only time to move into the 1mbar and lower region is distilling high molecular weight solids or running things like spectroscopy.

Resin & composite pumps are often overrate in terms of CFM for glassware work. They're designed to pump huge amounts of gas as it foams off, which isn't an issue in chemistry as you'll be condensing the gases and vapours that boil off, reducing the CFM to effectively 0.

In short, even if it's well worn, it'll almost certainly be fine for distillation work and similar.

[Edited on 3-8-2010 by peach]

mnick12 - 2-8-2010 at 15:22

You are right to warn me, and yes I dont much at all about vacuum pumps. That is sort of the reason why I started this thread so people with more knowledge could help me out.

Though I do have a good amount of experience with aspirator distillations. Most of the distillations I have done with aspirators is nitric acid and various solvent recovery type things. Oh and I probly wont use the pump for liquid distillations, but there are some phenols I have had trouble distilling with my aspirator. I will also probably use the pump for vacuum filtrations as well.

Thanks for the help.

peach - 2-8-2010 at 21:07

Think you'll be fine with it, and obviously have some experience with things that suck.

My only word of caution would be to consider putting a trap between the pump and filter flask. I've had oil from my rotary back flow to a filtration that was part of a weeks worth of work, everyday and into the night. Switching the pump off whilst the filter flask is under vacuum is a good way to encourage it; when the cake is blocking up the funnel. Disconnect the hose and then turn the pump off instead.

SWilkin676 - 3-8-2010 at 14:24

If anyone is looking for a good all round chemistry pump, I highly recommend the Savant 100-110 series gel pumps. I just bought my second one for less than a hundred bucks shipping in auction because the first one is so good we fight over it!!

We have a heavy duty leybold that can do a serious vacuum, but it takes a 1/2 hour to warm it up and uses a lot of power. Not what is needed when you just want to do a quick vacuum filtration.

The gel pump is pretty simple and reliable, the vacuum is more than adequate to get an alcoholic mixture boiling at room temp and can handle being switched on and off while you're trying to prevent an overboil. (husband says I got to get a manifold set up!)

Suzee

peach - 3-8-2010 at 14:38

Husband is right, and I need one too.

To be fair to the old rotarys, they don't need 1/2 an hour to warm up for a filtration. Perhaps a steady reading on a distillation, but a filtration doesn't need anything like that. I've owned three, and all three (be they 10CFM or 1CFM) will reach 1mBar or less in seconds, which is 99.9% of the atmosphere gone.

As an example of the warm up, I have just finished rebuilding an Edwards pump. I had the entire thing on bits all over the floor, every single spring, washer, nut, bolt, screw, seal... everything. I was using DCM and acetone to clean the insides. I also used KOH and 98% sulphuric to get the thicker grease off, before washing it all off with the hose.

I've literally only just put it back together and have it running overnight (it's humming away right now) to bed in and check it's okay.

Within a second or two of flicking the power on for the first time, the pressure went straight down to 0.158mBar. In around 4 hours of continuous running, it's only dropped to around 140mBar, 0.018mBar lower. Average atmospheric pressure at sea level is 1013.25mBar, meaning this change in vacuum level equates to a 0.0018% variation with regards to it's full spectrum... not a lot; especially considering what had been done to it prior to turning it back on. I'd be hard pressed to see that make any difference even in a number of distillations.

[Edited on 3-8-2010 by peach]

mnick12 - 5-8-2010 at 15:14

Well I shipped the monster home today, and the beast weighs a littile over 26lbs. It still needs a new power chord and some more oil, but I sanded off the rust and painted on some new "rust proof" enamel. So while it may not be the best pump, a free pump (shipping+repair) is better than coughing up $X00.00 for a new pump.

So when I get home I will try and distill some 4-methoxyphenol.

peach - 5-8-2010 at 17:22

Can't argue with a free price tag, unless you're buying a kick up the ass. And some people will pay good money for that too, kinky bastards <--- 100% not me :P

Anyway, I thought you might like the following pictures. Soon after receiving it, the pump built a cocoon and began hanging from the ceiling, purring at night and singing to me in my dreams using some inexplicable psi ability that isn't listed under the normal features. Later that week, it emerged and had undergone a beautiful tranformation to it's Optimus Prime battle mode. She needs a new baseplate before she can leave the nest, but that develops in the second week of the maturation phase.

I also have my Alcatel in bits at the moment. I have hundreds of pictures which I'll sort through and post up when my computer stops having a fucking seizure.

I hope the product you've purchased sucks hard. Not many times I can say that and have it mean something positive.



mnick12 - 9-8-2010 at 18:34

Nice,
When my pump arrives I will go ahead and post some pics of the ancient beast. Which reminds me, there was another pump which one of my antiquing relatives showed me. The thing is scary it is a huge motor with two cylinders,two belts, and uninsulated-nongrounded wires:o. There was no way i was going to plug that ancient sucker in, besides people actually like one and I didnt want it to burst into flames while arcing,

peach - 9-8-2010 at 20:03

Quote: Originally posted by mnick12  
Nice,
When my pump arrives I will go ahead and post some pics of the ancient beast. Which reminds me, there was another pump which one of my antiquing relatives showed me. The thing is scary it is a huge motor with two cylinders,two belts, and uninsulated-nongrounded wires:o. There was no way i was going to plug that ancient sucker in, besides people actually like one and I didnt want it to burst into flames while arcing,


YOU BIG GIRL'S BLOUSE!

PLUG IT IN! :P

Nah, but seriously... connect a fk'ing earth first... :D At least one.

And remember, one hand in your pocket. The old, and laughably (at first), rule of the high voltage folk; one hand in your pocket means the current is quite unlikely to pass through your heart, which is what matters (unless you kiss the pump at the same time). Plus a breaker, if only to avoid burning the windings out.

I'm not entirely sure why they switched from belt drives to direct drive.

Using some logical reasoning, I expect it's because the old pumps were typically single stage, to save on the machining costs. And that they'd run them with a ratio on the pulleys to develop more torque at the pump head without having to spend money on the (at the time) costly motor windings.

Now we can machine bulletproof, molding steels as standard, it's easy to produce dual stages and it's easy to produce high power motors.

I've never owned one of those old Welch single stages. The faceplates on similar pumps suggest 0.5mBar. That's not a million miles from the pressure most modern dual stages can achieve. They claim much better but, once they've been run for a while, they're around 0.5 to 0.05mBar, not 0.001mBar. I expect a lot of the 0.001mBar claims are theoretical, or fresh out of the factory. And rapidly decline to the stable 0.5 to 0.05mBar range. Never had the £2.5k needed to test that theory.

Besides, what's important is what it can achieve. Atmospheric is around 1013.5mBar. An aspirator is around 35mBar, as is a fridge compressor (which can do down to 13 mBar if you change the oil). A vacuum cleaner is around 750 - 800mBar. With my mouth, I can pull around 200mBar. Most solvents begin boiling at room temperature at 100 - 35mBar. Meaning, there's not much need to go sub mBar until you're running analytical equipment (diffusion plus for mass spec etc, e.g. turbo, ion, and so on).

At a mBar and less, you'll actually end up trying to bleed gas into the system to get the solvent liquefying above 0C a lot of the time, if yars be being smart. If not, you'll opt for buying more glass and cryogenic coolants.

[Edited on 10-8-2010 by peach]

jwarr - 10-8-2010 at 00:03

While we're on the subject of vacuums, do you guys get your oil online or off? I'm looking for a brick and mortar store where I can buy vacuum oil in a pinch.

peach - 10-8-2010 at 03:49

I scrape mine off the fat girls down at the gym.

When they're out at KFC, porking, I have to buy it (security have barred me from most fast food chains), and it's not available from normal public stores here. Saying that, if you look at my dry ice thread, you'll see not only dry ice isn't available cheaply here (by the scoop), neither is normal ice (in premade bags). I can, however, buy a big sack of sublimated iodine if I want with no paperwork involved, and it's perfectly legal.

densest - 10-8-2010 at 08:10

Piston pumps still use belts. The load is cyclical and the belt evens it out a little bit and the mechanical advantage is useful as well. Rotary vane pumps present a much more even load on the motor and can run at high RPMs so they can be direct drive. Graphite vanes weren't practical until relatively (20-30 years?) recently.

peach - 10-8-2010 at 18:03

Thanks for the info densest. I know I've seen recent workshop compressors (pistons) still using belts. I have seen a direct drive from Ingersol Rand (the Nirvana), but that's a rotary screw. And a very sexy, expensive bit of kit it is.

I've been mutilating a number of fridge compressors this week to find out precisely what's going on inside the more modern ones. In the schematics of them I'd seen, there was simply a coil inside and a tiny piston that vibrated in it's core, a solenoid in effect.

Once Dr Angle Grinder had done it's toasty hot work on the casings, I discovered something quite different. In the samples I opened, there's a motor winding roughly the same size as the can inside, with an iron casting bolted to the top side of the winding / core. There is only one bearing surface, where the rotor passes through that casting (none on the bottom). On the other side of the casting, there's a little eccentric, which is connected to a cam shaft (now going horizontally). That drives the equally tiny piston.

Interestingly, no seals. Other than what appears to be an oil capturing seal ground into the piston head. Also of interest is that the rotor is a hollow, thin walled tube that pokes down into the oil sump at the bottom (there's only around an inch of oil in there). There's a hole in the bottom of the rotor and it appears to function as it's own oil pump, sucking oil up the centre of the rotor and then spraying it out of strategically positions holes at the top (where the eccentric is). But barely any of that is destined for the piston it's self (unlike a rotary, who's oil pump sprays it directly into the vane chamber.

I made some videos of me doing this, comparing it to my rotary and using it for a filtration, as well as some other comparisons. I'll post it up once I've had a chance to find some means of connecting the clips together (in Linux, I'm also not a big fan of video editing either).

Do all vanes now have some degree of graphite in them? The ones I've seen have reminded me most of phenolic / bakerlite plastic. Hard, tough and smooth; the kind of thing that'd split if struck with a hammer, as opposed to deform.

I know commercially, we can buy brass / bronze that's been sintered and hydraulically impregnated with oil for lifelong lubrication, so adding some graphite to a friction bearer makes sense as well.