Buy vacuum pump for degassing chamber

Alfr3d

New Member
Hello there :)

I want to buy a vacuum pump for a degassing chamber that I purchased a few days ago relatively cheap. It is a 17 L or 4.5 gallon degassing chamber which you can see right here:

https://goo.gl/sh1Gyg (sorry for the German amazon link, that is where I live and I was not able to find an amazon.com link)

Now is the question:
What specs should a vacuum pump for that chamber have(or doesn't the size matter ;))
I am currently looking at this pump, because I can get it for a relatively low price at a local shop:

https://goo.gl/Z5wGFw

Specs:

* 3 CFM
* 85 L/Min
* 1 Pa
* 2800 Rpm
* 150 ML
* 1/6 HP
* 1/4'' SAE
* 220V 50HZ

Is this enough to degassing some silicone?

Btw this is the project I am currently working on:

20170131_195345.jpg


Thomas (But not Bangalter)

20170131_195345.jpg
 
Last edited by a moderator:

19narvik40

Sr Member
I have been told that the main difference between the 3 CFM vacuum pump and one with a higher rating is time. Using a 17L (4.5 gallon) vacuum chamber means there is a lot of air it has to evacuate. The big issue is what is the setting time on your silicone once it is mixed. If you are using a fast curing silicone, you may run out of time to mix, degass and pour the silicone around your mold. Hope this helps.
 

cavx

Master Member
The biggest you can afford.

My chamber is 30 litres. My first pump was 3cfm and it took 3.5 min just to vacate the air.

My current pump is 9cfm and it empties my chamber in just under 1min.

What you also need to consider is the pot life of what it is that you are degassing. Typically 2 min under full vacuum will work on most resin. But that time is added to the initial vacate time and comes off the potlife. If that makes sense.



Sent from my SM-G900I using Tapatalk
 

clonesix

Master Member
My answer is NO. I am going on the assumption that you are degassing Silicone RTV? None of the specs listed above list the vacuum that it produces. You need as close to 29 inches of Mercury. You are not just drawing a vacuum, you need to draw a big enough vacuum to release the air from a very viscous fluid, before it begins to solidify. RTV takes 24 hrs to cure, but you really only have 30 minutes.

The two things that I get from that ad are: 1/6 HP and "single Stage". Neither of those will help you. 1/3 HP min to 1/2 Hp, and Dual Stage for higher vacuum.

I hope this helps

These (refrifgeration) pumps are more expensive. I spent $160 on a Robinaire 6 cfm. It works fine, but in retrospect, I could have gone bigger.
 

Alfr3d

New Member
Ok... I think that this gave me a good impression of what i should be looking for. As i will do some vacuumforming the next time more power is better...
Currently i have this model in mind... Super overpowered... But super cool also!

http://www.ebay.de/itm/371380385468

-8 CFM
-0.3 PA
-1 HP

Thanks again for all your help!
 

cavx

Master Member
Ok... I think that this gave me a good impression of what i should be looking for. As i will do some vacuumforming the next time more power is better...
Currently i have this model in mind... Super overpowered... But super cool also!

http://www.ebay.de/itm/371380385468

-8 CFM
-0.3 PA
-1 HP

Thanks again for all your help!

Do a search and I am sure mobs like these make pumps up to 12cfm. Mine is 1HP/ 9cfm / 2 stage. 8cfm will rock on your chamber and that price is good.

When I was buying mine, I knew to buy locally, a 9cfm pump was $1100. I searched on line and found similar pricing. Then I found a sale of 20 units on eBay. They too were $1100 each with 20 availlable, 0 sold. So I added it to my watch list and kept checking up on it. What I found was that that every time they sold a pump, the price on the remaining stock dropped. When I bought mine, it was 18 sold, 2 available at $219 each! I I quickly checked the other bookmarked site to see the same pump at $1100 and clicked the BUY IT NOW on that eBay page! I should have bought both.

2 stage pumps run a far bit quieter than a single stage but they also are said to pull deeper. What ever that means because no domestic pump I've seen does greater than 1 x 10^-3.

EDIT or is that 3 x 10^-1?

It would be awesome to get a 1 x 10^-6 or twice a negative atmosphere. There would be NO bubbles left.

What you will notice when you degas is that even at -30"Hg, bubbles form and pop as the contents under vacuum boils away, but there are bubbles in the mix that seem to never pop. When you re-pressurize, the sudden increase in pressure crushes most of them anyway. But wouldn't be better to pull them all out?

With the Silicone I use, the stuff raises and falls at least 3 times and then it looks like dish soap with big bubbles that will not pop at 30"Hg. Again, re-pressurizing crushes them and because the product I like to use has a 6 hour cure time, any bubbles still left in the mix tend to rise to the surface.

I know that pumps (bigger than a car) are used in the Sugar mills north of me that pull 1 x 10^-9!
 
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Alfr3d

New Member
Do a search and I am sure mobs like these make pumps up to 12cfm. Mine is 1HP/ 9cfm / 2 stage. 8cfm will rock on your chamber and that price is good.

Well, what can I say...that pump I bought(1HP, 0,3Pa, 8CFM) is totally cracy! Without oil in it it is three times the weight of my older pump, with oil in it (IT NEEDS SO MUCH!) it weights probably more then 4 times as much. It is very big and very loud.

When I connected my vacuum chamber I was amazed by how fast it sucks all the air out. This thing isn't a joke. This is the real deal, a monster.

I am super happy with my purchase, this thing is future proof.

Btw: there is not such thing as a vacuum that can pull 30 in of Mercury. Not even 100% vacuum can do that. I think, my pump comes up to about a 99.9997% Vacuum... WTF

Thanks again for your help!
Thomas :D

This site is really helpful:
http://www.engineeringtoolbox.com/vacuum-converter-d_460.html
 

cavx

Master Member
Cool. Look forward to seeing some bubble free parts.

Also look up PU shoes on YouTube watch how fast their vacuum systems work. That is crazy stuff.
 

cavx

Master Member
Yeah just checking the chart, a full vacuum is 29.92"Hg. On an analogue gauge, that would look like 30".

Sent from my SM-G900I using Tapatalk
 

cavx

Master Member
Can you use a tank from a compressor, lower it to the max the pump will pull then use it to quickly draw the vessel to that level?

Like a surge tank? I guess you could, but you would want the pump running the entire time to make sure the tank is kept at vacuum and the chamber you open to the atmosphere would need to be small or wide and very flat.

I can't seem to find the video now, but there was video from a China PU shoe factory that, once the operator closes the lid, instant vacuum. The gauge whips around to max suction. It was impressive to watch.
 

VisualConduct

New Member
Ok... I think that this gave me a good impression of what i should be looking for. As i will do some vacuumforming the next time more power is better...
Currently i have this model in mind... Super overpowered... But super cool also!

http://www.ebay.de/itm/371380385468

-8 CFM
-0.3 PA
-1 HP

Thanks again for all your help!

Thats looking good.. I am a complete noob to this and I want to buy a pump for degassing.
But 0.3 Pascal, isn't that a insufficient pull, I saw that at least 29 inch of mercury is required.
Probably something I don't understand :) Maybe the 0.Pascal is what is left?
Would be good to have some chart with all the conversions and their meaning.

Kind regards, Robert
 
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cavx

Master Member
Thats looking good.. I am a complete noob to this and I want to buy a pump for degassing.
But 0.3 Pascal, isn't that a insufficient pull, I saw that at least 29 inch of mercury is required.
Probably something I don't understand :) Maybe the 0.Pascal is what is left?
Would be good to have some chart with all the conversions and their meaning.

Kind regards, Robert

I wish we were all on the same page when it comes to vacuum. I use inches of mercury as that is an easy figure to understand. A vacuum specialist kept throwing in the term bar. As it turns out, 1 bar is 1 atmosphere. A full negative atmosphere is 29.5"Hg, but you need 30"Hg continuous draw to degas resin or silicone rubber. You have to draw the bubbles up and out. If it was possible to buy a negative 2 atmosphere pump, it would be better, but I don't think such a beast exists.

My first pump was only 3cfm, 0.5hp, single stage. For a small chamber like a 1 gallon, it takes about 45 seconds to reach 30"hg.

My 2nd pump is a 9cfm, 1hp, two stage and it takes my 6 gallon to full vacuum in just on a minute.

I'd like to see how fast it can pull a vacuum in the same 1 gallon pot.

I am currently using the big pump as part of the vacuum former now and it can pull that massive chamber down to vacuum quite fast. I don't take it much past 20"Hg though.

So buy the biggest pump you can afford.
Mine has two different size connectors, so I can connect a smaller 1 gallon pot to it if I need to degass small amounts of resin.

Sent from my CPH1701 using Tapatalk
 
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VisualConduct

New Member
@ Cacx, Thanks a lot for your prompt help :)

My main concern is that I am unsure if 0.3 pa is sufficient for degassing.
On the other hand I also consider doing lost wax vacuum casting, so trying to investigate what specs I will need for that.

Regards, Robert
 

cavx

Master Member
@ Cacx, Thanks a lot for your prompt help :)

My main concern is that I am unsure if 0.3 pa is sufficient for degassing.
On the other hand I also consider doing lost wax vacuum casting, so trying to investigate what specs I will need for that.

Regards, Robert

Your welcome.

I don't even know what 0.3 pa stands for.

What you need is -30"Hg. That pulls bubbles. Tried and proven.

But also, you need to get there fast, so buy the biggest pump you can afford. A 2 stage is better than a single and I wish I had bought the 12cfm pump now. I found it about a week after buying the 9. The higher the cfm, the faster you reach that needed -30"Hg and the better the result.

Do a search for local suppliers, look on eBay. Here in Australia, a 9cfm, 2 stage pump is $1100. I found a guy in Sydney with 20 for sale at $1100each. I added it to my wish list. I checked it every few days. Every time he sold a pump, he dropped the price. I ended paying just $217 + $28 shipping on eBay for brand new unit.

Enzed got me on the hoses at $450.

EDIT: Just googled it now and pa is pascal, but based on the meter, so you need 0.76pa, not 0.3. Because 30"Hg is 76cmHg or 0.76pa.
 
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MachTig

New Member
Well, what can I say...that pump I bought(1HP, 0,3Pa, 8CFM) is totally cracy! Without oil in it it is three times the weight of my older pump, with oil in it (IT NEEDS SO MUCH!) it weights probably more then 4 times as much. It is very big and very loud.

When I connected my vacuum chamber I was amazed by how fast it sucks all the air out. This thing isn't a joke. This is the real deal, a monster.

I am super happy with my purchase, this thing is future proof.

Btw: there is not such thing as a vacuum that can pull 30 in of Mercury. Not even 100% vacuum can do that. I think, my pump comes up to about a 99.9997% Vacuum... WTF

Thanks again for your help!
Thomas :D

This site is really helpful:
Vacuum Pressure - Units Converter
You bought the vacuum pump that I got my eyes on at the moment. I am being tempted with lower priced pumps and it seems too big of a risk to take with most, my guess most will have a short life. Are you still happy with your purchase?
 

ScoobiJohn

Active Member
i wouldn't go cheap - i bought a cheap setup and i was not only slow but i couldn't pull enough of a vacuum - got down to about -28"Hg and it jsut wasn't quite enough - so bought a better pump and suddenly everything worked great - cant actually remember the specs but it was much faster and managed -30"Hg
 

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