Something other than a vacuum pump?

General Composites Discussions Equipment Talk
#1

Hello all,

I’m trying to price up the equipment I need to start making some carbon parts properly. I’ve got on my list I’ll want an air compressor (not a clue what size I’ll need) for an air sander to help finish the edges of the parts I make.

What I’m wondering is - is it possible to use the air compressor and a venturi pump to vacumm bag parts? I could have sworn I read somewhere this was another method without needing a vacuum pump.

Or will it be better to get a proper vacuum pump as the results will be superior?

Any opinions/experiences welcome.

Thanks :slight_smile:

#2

I’ve used a venturi vac genny in the past with no probs. You just need to ensure your compressor has enough capacity to run continuously unless you put in a vacuum check circuit in so it only runs to top up the vacuum.

#3

Even though it’s possible to use your compressor for vaccum I wouldn’t recomend it cause the compressor will run all the time in order to create the venturi making it hot and noisy. The best solution is to get a proper vacuum pump.

#4

Thanks for the replies.

You make it sound like the vacuum would need to run throughout the whole time the part is curing? I thought you could suck out all the air and put the part in the oven - without needing further vacuum pressure? Afterall, once the air is removed then surely that’s enough?

#5

That would be the ideal case scenario, but often you need to have the pump on stand by in case the pressure drops.

#6

No, you always need vacuum. Because even if you somehow have a perfect bag, once heated, the tackytape might soften and shift, part might exotherm and melt the bag, and in ALL cases, no matter the resin…it will outgas, even if slightly, will then cause a lack of vacuum pressure.

#7

Creating vacuum with a compressor is way more expensive than using a pump. I would opt for a (2nd hand) industrial pump, not an airco pump. With a bit of luck and perseverance you can have a decent unit for less than 500 dollar. (including buffer tank and switch, so the pump does not run continuously.)

#8

Thanks for the replies.

Looking on the Rietschle website and there are several different varieties of pumps - rotary vane, rotary lobe and claw. Which is better suited to vacuum bagging composites? Also are there any key features I should look for with the pump? (e.g should it use oil)

I also found this site which specifies the pumps as being for composites

http://www.girovac.com/page.asp?id=55

#9

Those pumps in that link are going to be a bit expensive, and are VERY large. I use a Gast SAA-V109-NQ which is 1.3cfm open rate, and gets down to 29.6"hg. Try to get a DRY pump, not oil filled. Although, I have used oil lubed rotary vane before, and didn’t have any oil misting issues, since the oil is separated from the vacuum system. The Gast i use is a dual rocking piston pump, works well since you can run it open for as long as you need. The airflow is small (they have bigger), but I don’t have an issue since my parts are no bigger than a coffee table. Airflow only means how quickly it sucks out the air in the bag in the start…if you don’t care about a 5min pumpdown, no reason to get a bigger pump.
so, key features: Dry pump (diaphram, vane, piston, lobe maybe) that gets down to 29" at least, and has 1-3cfm airflow, unless your plans are LARGE parts. go 3-5cfm. If it does not come with an inlet airfilter, you can get a small pleated one from them, or elsewhere…keeps any dust/fibers out of the pump!

#10

Excellent riff. Thank you.

I may make the occasional large part, but that’ll be once in a blue moon, so having to wait for the air to be evacuated won’t bother me.

That Gast pump seems to be a really nice compact size looking at the dimensions of it. Here is the PDF file of your pump http://www.gastmfg.com/pdf/rockpist/specsht/saa.pdf

In the list of recommended accessories (next to the top picture in the pdf link), they list a vacuum guage and also vacuum relief valve - which of those (if any) would you suggest would be worth getting?

#11

If you opt for a Rietschle / Thomas pump, go for a VCE or VCA model.

You can turn the pump into a vacuum system by adding a pressure switch and a tank. That is basicly what the Compositvac units are, and also what I build for customers. (although my systems are fully enclosed in a trolley. You could smash them into a wall, without stuff breaking off…)