I teach h.s. woodshop and am going to get us set up to do bag clamping and veneering. I have been researching systems and have found two basic kinds: pumps vs. compressed air.
First of all, do the compressed air systems use a steady supply of air or do they use the air to pull a vacuum and then hold it? Is there the constant stream of air blowing and making noise?
Are vac pumps easier to use for hold down clamps & fixtures as well? Also which is more reliable? It will be used almost constantly once we get set up.
I guess what I am after is some guidance with personal experience. I sure would appreciate any help.
Replies
I use a Bernoulli/Venturi devise (a single stage vacuum generator) and run it using compressed air. I expected it to be very noisy but I was pleasantly surprised at its relatively low noise level. The unit I bought came with a small muffler. Based on my experience with small aquarium pumps, the noise level was only slightly greater and I would guess about comparable to what I think a vacuum pump might produce. (It has been a while since I used a vacuum pump - running a vacuum oven, but they seem to be not all that quiet if my memory is correct).
Whether you have to run it consistently or not will depend entirely on the "air" tightness of your vacuum bag. My bag is tight so that the last time I used it, I pulled a vacuum, closed the added shut off valve (between the bag and the Venturi devise) and it held for at least 24 hours (when I came back and opened it up).
My bag is approximately 3 x 4+ feet. I would estimate it took less than 3 minutes to "completely" evacuate it.
There are two primary benefits, in my thinking, that swayed me to a vacuum generator (over a vacuum pump). The first was the cost. I have a Gast VG-010-00-00 that will pull a max of 27" of mercury @ a flow rate of 0.95 CFM; it cost me about $50.00. (The added cost of a quick release fitting, some tube fittings, hose clamps, a valve and tubing may have added another $12 to $15. That total price was about 1/4 of what a comparable level vacuum pump would cost. Secondly, a vacuum generator is virtually maintenence free. And it is very easy to store because it is almost laughably small.
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