CFM requirements for vacuum bagging

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#1

I’m unclear on the CFM requirements I might need in order to vacuum bag a large tube measuring 12" x 36" x 0.06" wall thickness. A document provided by Soller Composites states that a pump capable of 1 CFM is suitable for small projects and more CFM is required proportionately for larger projects.

If I were to use a 1 CFM pump that provides say 24 PSI for bagging my large tube, would it simply fail to fully evacuate the bag, or rather would it succeed but require a much longer period of time to reach that point?

After shopping for pumps I can’t find any that produce more than a couple CFM for less than $3K. That is totally cost prohibitive for me. I am hoping to find a pump solution that is capable of bagging a large tube like I’ve described and is yet affordable on a small business budget.

#2

Assuming a leak free bag a low CFM pump would eventually reach it’s full vacuum but at a much slower rate. One trick commonly posted is to use a vacuum cleaner to get most of the air out then let your low cfm pump do the rest.

If there is a leak though a low cfm pump won’t be able keep as much. The analogy would be this. If you’re in a canoe and you have a pin prick leak an aquarium pump would remove water easily. If you had a fist sized hole though it would be overwhelmed.

#3

Thanks that makes a lot of sense.

I just learned about the vacuum pumps that attach to an air compressor. As an example, McMaster Carr sells one with the following specs:

Max Hg = 28"
Free air CFM = 9
Operating pressure = 80 psi
CFM at operating pressure = 12.5 CFM
Cost = $166.29

Would something like that work?

#4

I have no idea of the pumps available in the USA, but for 3K you can buy a big ass pump.

Check the refrigerator and airco section for reasonable priced pumps. You might need a vacuum regulator if you do not want the “full pull”. Check Airtech VAC REG for that.

#5

Sorry I should have been more specific. When I said 3K I meant that I cannot spend anywhere near that much.

#6

look at the 3 cfm pump at harbor freight.that is what i use.it works great on large parts.plus you can buy there extended warranty.i have used mine for a year now with no problems.they are always on sale for 149.99$

#7

venturi pumps aren’t efficient in any way, since you need alot of air to pull a vacuum!! you can get a good Gast for 500$, and many cheaper ones, and cheaper used ones.
try to get soemthing as high a vacuum as possible!

#8

Thanks I just checked it out on the HF website. It says 3CFM but it doesn’t give the psi or inches Hg. Any idea what those specs are for this pump?

#9

No idea what that particular pump pulls but I have the smaller 1/6th hp one and it pulls 28 inches of mercury. The thing spits oil like crazy though if there’s a leak so be prepared to put it outside or somehow contain the mist. There is no obvious outlet on mine so I am unable to filter the exhaust but other than that the pump works great especially for its price.

#10

I am sorry for being in the Netherlands, but over here I have pumps that are in the range of Euro 150-250, drawing a near full vacuum, these are oil lubricated rotary vane pumps. Indeed oil spitting, but I can install filters if people like that. (life of the filter is limited).

For some 500 euros one can buy an industrial pump, with more cfm and regenerating filters.

Pumps in the 3K range are out of my range. These are so big they do not fit on the trolleys we manufacture (the trolleys should be able to pass through normal doors…)

I also have a very small dry vane pump, drawing 85% of vacuum, and which is very quiet. I use them for demonstrations mostly. Cost is some 250-300 euro I believe. Size is perhaps 6x6x8 inch.