Sciencemadness Discussion Board - is this a good vacuum pump?

is this a good vacuum pump?

Pyro - 19-7-2012 at 13:56

hello,
i found this air cadet-Cole Palmer vacuum pump for 150 EUR
its specifications are:

Max vacuum 20" Hg
Max pressure 18 psi
Free-air capacity 0.5 cfm (14.1 L/min)
Port size 3/8" hose barb
Motor type 1/45 hp, TEFC
Max temperature 95°F (35°C)

is this a good deal?

DJF90 - 20-7-2012 at 01:49

Get yourself a water aspirator. They'll do better than this for the same thing for a lot less money. For a high vaccum source, you're probably after a 2 stage pump of 2-5cfm capacity, and ultimate vacuum in the 10-25micron range. For simple lab vacuum, say for distillation under reduced pressure, or vacuum filtration, an aspirator is usually sufficient, with the added bonus that you don't have to worry about corroding the crap out of it. The specs you're providing suggests that pump pulls down to about 220mbar ultimate pressure. I dont think this is enough for the cash you'd be paying. An aspirator will easily get down to 50mbar, and really good ones can go lower. It also depends on the temperature (or rather, vapour pressure, which is a function of temperature) of the watter passing through it, so use as cold a source as possible. A friend of mine had a 50L bin filled with water and hooked up to a pump to recirculate and avoid excessive water bills.

adamsium - 20-7-2012 at 02:04

Quote: Originally posted by DJF90

Get yourself a water aspirator. They'll do better than this for the same thing for a lot less money. For a high vaccum source, you're probably after a 2 stage pump of 2-5cfm capacity, and ultimate vacuum in the 10-25micron range. For simple lab vacuum, say for distillation under reduced pressure, or vacuum filtration, an aspirator is usually sufficient, with the added bonus that you don't have to worry about corroding the crap out of it. The specs you're providing suggests that pump pulls down to about 220mbar ultimate pressure. I dont think this is enough for the cash you'd be paying. An aspirator will easily get down to 50mbar, and really good ones can go lower. It also depends on the temperature (or rather, vapour pressure, which is a function of temperature) of the watter passing through it, so use as cold a source as possible. A friend of mine had a 50L bin filled with water and hooked up to a pump to recirculate and avoid excessive water bills.

I actually want to do precisely what your friend did in terms of using a pump in a tub for recirculation of water through an aspirator. Do you know roughly what flow rate would be required? I have the aspirator, but I don't really have a tap that it will connect to, nor is there a tap near where I plan to work. If I could connect the aspirator to a tap here, I'd simply get it running with a decent vacuum and measure the volume of water that passes through it for a certain period of time in order to determine a flow rate. If you can give me a ballpark figure, that would be great as I can avoid buying pumps hoping that the flow rate is sufficient / not too high.

Hexavalent - 20-7-2012 at 09:46

Opinions on this;

http://www.ebay.co.uk/itm/Vacuum-Hydro-Pump-aspirator-for-di...

I once received a metal aspirator that needed the outdoor hose on full blast to obtain even a tiny vacuum....

adamsium - 20-7-2012 at 22:25

Quote: Originally posted by Hexavalent

Opinions on this;

http://www.ebay.co.uk/itm/Vacuum-Hydro-Pump-aspirator-for-di...

I once received a metal aspirator that needed the outdoor hose on full blast to obtain even a tiny vacuum....

That aspirator looks exactly like the one I have. Here is a photo of mine:

I'm hoping I can get it to pull a decent vacuum using a pump like DJF90 mentioned his friend has done. This could be difficult if it requires a flow rate like the metal one you describe.

Is there anyone who has experience with this particular aspirator (or similar) and can give an idea of the flow rate that it requires?

Pyro - 21-7-2012 at 05:29

ive got one of those, i just feel like moving up a little. should i stay with this instead?
(now i just hook it up to the water coming out of my condenser. its in the container that my cooling pump is in)

Hexavalent - 21-7-2012 at 09:39

How does it perform, guys?

Pyro - 21-7-2012 at 10:07

what? the aspirator?

chemrox - 21-7-2012 at 12:09

I have an aspirator that boils water at room temperature with no problem at all. Based on the boiling temp of aniline it plotted at 18 torr. I've had metal ones that struggled to hold a filter paper in place. I have an aspirator pump that recirculates water and runs two aspirators. It goes to around 10 T. I use it with the rotovap and run the rotovap condenser water through the pump reservoir keeping vapor buildup down. Mechanical pumps require vapor traps, air filters, ballasts, etc. Not to mention lots of pump oil.

watson.fawkes - 23-7-2012 at 07:29

Quote: Originally posted by adamsium

Is there anyone who has experience with this particular aspirator (or similar) and can give an idea of the flow rate that it requires?

You can just measure it. Get the aspirator working at an adequate pressure. Then use a bucket and stopwatch.

adamsium - 23-7-2012 at 15:28

Quote: Originally posted by watson.fawkes

Quote: Originally posted by adamsium

Is there anyone who has experience with this particular aspirator (or similar) and can give an idea of the flow rate that it requires?

You can just measure it. Get the aspirator working at an adequate pressure. Then use a bucket and stopwatch.

Yes, that's the problem. I don't have a tap that I can really connect it to (at home, anyway), which is one reason I plan to use a pump which will be easier to connect with appropriate tubing. I used that exact method to decide the rough flow rate I needed for a pump for condensers - knowing I don't need much more than a trickle, I set the tap to a trickle and filled a 1 L jug whilst timing it.

If someone could at least give a ballpark figure (I've never used a vacuum aspirator of any type before - I'm used to having vacuum on tap!), it might well save me wasting money and time buying useless pumps, that's all. I have no idea what sort of flow rate they need, though I'd guess it's probably more than you'd want running through a condenser.

Siggebo - 26-7-2012 at 06:07

Around 6 liters per minute seem to be the ballpark, according to several lab suppliers' websites.

Also, first post I believe!

polymerizer87 - 26-7-2012 at 09:48

Son, for 20'' Hg get a water aspirator like DJF90 says. I've used a 1,500 USD vacuum pump in the lab and the water aspirator did the same job on a vacuum filtration i was doing with activated carbon.

Dave Angel - 26-7-2012 at 11:23

As I was describing in another recent pump thread, I have found a chemical resistant diaphragm pump to be my go-to device for vacuum.

I don't have a water tap inside my 'lab' (as far as one can call it a lab these days), plus I find running water down the drain to be wasteful. I have most of the parts on hand to build a recirculating water pump for this, but it's another low priority project waiting for some free time and space.

My personal experience is that plugging in and switching on the diaphragm pump is so much more convenient than handling a water aspirator. If I had a nice lab set-up with un-metered running water, or a neat recirculator build, with vacuum lines piped around the workspace, then I might have a different opinion.

Again, it's a different matter if one is, say, distilling something really corrosive, in which case it's worth setting up the aspirator, but it's frankly a pleasure to be able to put the diaphragm pump anywhere I need it and have it going in seconds.

If you do go for the latter type though Pyro, aim to get one that has PTFE parts to ensure good resistance for most purposes.

This all of course depends on your budget, so good hunting.

[Edited on 26/7/2012 by Dave Angel]

Pyro - 26-7-2012 at 11:28

hello,
i found a plastic one for 10 EUR 7 EUR i can buy 3 glass ones. so ill stick with the aspirator

How to Make an Aspirator

cal - 19-8-2012 at 09:25

How to Make an Aspirator

This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do"

A simple aspirator that may be used for a number of different purposes, such as accelerating the process of filtering, emptying water from' tubs, producing a partial vacuum in vessels in which coils are being boiled in paraffin, etc., may be constructed as follows : Obtain two pieces of brass tubing of the following dimensions: one 7 in. long and 3/4 in. outside diameter, and the other, 3 in. long and 1/4 in. outside diameter. Drill a hole in one side of the large tube, about 3 in. from one end, of such a diameter that the small brass tube will fit it very tightly. Take an ordinary hacksaw and cut a slot in the side of the large piece, as shown at A. This slot is sawed diagonally across the tube and extends from one side to the center. Obtain a piece of sheet brass that will fit into this slot tightly, and then solder it and the small tube into the large tube. The slot and hole for the small tube should be so located with respect to each other that the small tube will empty into the larger one directly against the piece of sheet brass soldered in the slot.

:cool:

Ill: Detail of the Aspirator and Its Connections to a Faucet, for Increasing the Speed of Filtration

The upper end of the large tube should be threaded inside to fit over the threads on the faucet, or an attachment soldered to it similar to those on the end of an ordinary garden hose. A rubber hose should be attached to the small tube and connected, as shown, to a piece of glass tubing that is sealed in the cork in the top of the large bottle. The funnel holding the filter paper is also sealed into the cork. Melted paraffin may be used in sealing the glass tube, funnel and cork in place, the object being to make them airtight. The filter paper should be folded so that it sticks tightly against the sides of the funnel when the liquid is poured in, thus preventing any air from entering the bottle between the paper and the funnel. Turn on the faucet, and it will be found that the time required to filter any liquid will be greatly reduced. Be careful, however, not to turn on too much water, as the suction may then be too strong and the filter paper become punctured.

[Edited on 19-8-2012 by cal]

Tdep - 26-3-2016 at 20:22

Hello, I just noticed this on Gumtree near where I am:

http://www.gumtree.com.au/s-ad/aldgate/miscellaneous-goods/p...

This seems like a fantastic price but is it complete overkill for what I need it for? Vacuum filtration and distillation and all that. I have a feeling it is. My current set up uses a normal vacuum cleaner and it's a little bit of underkill and i'm a bit sick of waiting around for things to filter.

NedsHead - 26-3-2016 at 20:58

I don't think it's overkill, if anything it just means you can do more with it, I would make an offer and see what happens, I was fortunate enough to find a rotary vane vacuum pump at the scrap yard and take it home for free! I changed the oil and it's been running like a champ for a year now

I would pick the last one with a capacitor start motor

[Edited on 27-3-2016 by NedsHead]

Tdep - 26-3-2016 at 21:37

NedsHead I was going to text you about this deal but you're already way ahead it seems! What sort of numbers do you pull on your glassware, aren't worried about any implosion? Or do you use it for other things?

NedsHead - 26-3-2016 at 22:08

I can pull down to about 700mmHg, I think that's equal to 700 torr? it's no problem for my glassware even jam jars with a thick tin lid seem to handle that vacuum, nothing volatile of coarse, and I still squint behind the safety glasses haha.

I use it for filtration and and distillation. I have used it in the past to distil nitric acid and concentrate sulphuric acid but I stopped doing that because I want the pump to last

chemrox - 28-3-2016 at 17:30

I'd like to change from the aspirator pump (not aspirator) I'm using with the rotovap. It's not a bad setup. The condenser water flows through the pump to change the water and keep the thing from getting messed up with solvents BTSO of using a trap. I'm thinking in terms of a diaphragm pump. Comments? Also I routinely get confused by vac/pressure parameters. e.g. what is 24" water in cgs units? or compared with 24" Hg?

NedsHead - 28-3-2016 at 22:14

this online converter might help answer your questions http://www.theunitconverter.com/pressure-conversion/

Tdep - 9-4-2016 at 01:38

So I got the pump, it has a bleed value connector come with it so i'm not as worried about imploding the glassware now that I don't have to have it cracked to max at all times.

This is what it pulls just with some plastic tubing between the gauge and pump with the bleed valve fully closed. It should be able to do better than this right? If i'm reading the gauge correctly, it's mmHg from atmosphere (~760mmHg) so the 480 on the gauge is really 280mmHg overall. I was told it could get to 0.1mmHg, does that mean I should be able to get it to 700 on that dial?

NedsHead - 9-4-2016 at 03:12

The more I deal with vacuum pump pressures, the more confused I become, the vacuum pump you bought are able to evacuate A.C systems so it should be capable of pulling some decent vacuum, the gauge you’re using doesn’t look the best quality and maybe its not giving you an accurate reading?..

edit; if you're not sure about the gauge you could pull a vacuum on some distilled water and monitor temperature it boils at

[Edited on 9-4-2016 by NedsHead]

Ozone - 9-4-2016 at 04:02

Here's one. It's a diaphragm pump, so much more forgiving if you aspirate stuff into it. It is also oil less. They can pull 25.5"Hg (26 once broken in), and has bleeder valves for adjustment:

http://www.ebay.com/itm/GAST-VACUUM-PRESSURE-PUMP-MODEL-DOA-...

Here's one, stock:

http://www.coleparmer.com/Product/Gast_High_Capacity_Vacuum_...

O3

Alkoxide - 9-4-2016 at 05:45

You can definitely find some good deals on ebay. I bought a KNF 2 stage vacuum pump with PTFE heads and explosion rated motor, 29.7" Hg vacuum, for $175 with shipping (it weighed ~45 lbs). I originally bought an aspirator but my sink could not connect to it due to non-standard threads on the faucet. I love my vacuum pump, never had a problem with it and its probably older than I am! Vacuum pumps also have the bonus of an exhaust port that can be connected to tubing to remove toxic/corrosive vapors from the lab area. Aspirators carry vapors right through into the sink.

rsneha - 22-11-2018 at 00:31

Quote: Originally posted by NedsHead

this online converter might help answer your questions http://www.theunitconverter.com/pressure-conversion/

Also try this one : https://unitconverter.net/pressure-conversion