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Hello guys,
I have question about vacuum holding. I use vacuum pump with max -1bar / -30Hg.
My question is, if I connect pressure pot with tube 6mm diameter to holder with sucking area 5x5cm, is end holding power same if I use for example 15mm diameter tube ? Will it be same or much higher ?
Thanks
Hi,
ultimately the hold-down force will be the same. The 6mm hose will take longer for the vacuum to propagate throughout the 5 x 5 volume (plenum) than a 15mm hose.
If there is a leak, even a small one, the 15mm hose will pull down that leak whereas the 6mm may not be able to draw enough to prevent the pressure rising slightly
in the vacuum plenum.
I used to make vacuum bagged wing cores for model areoplanes. I had an old refrigerator pump for the vacuum, but found I needed a large vacuum ballast to prevent continued
re-starting and cycling of the pump. I uses an 80l LPG cylinder. I had 6mm tubes connecting the pump to the ballast and the ballast to the vacuum bag. You can imagine it took a while
to pump all the air out of the ballast through such a small pipe, about two minutes....so hardly objectionable. It would take no longer than a few minutes to pump down
the vacuum bag and its contents and the ballast. Once you'd gone around and tweaked the enivitable little leaks in the bag the whole lot would sit for 24 hours while
the epoxy cured. It would be lucky for the pump to cycle more than three times and for about 30 secs each cycle. No trouble.
If you were trying to vacuum dry some organic material where you could expect a high vapour load, or you have an imperfect vacuum plenum then you'll need a 15mm pipe,
but for a good vacuum plenum with little or no vapour load then 6mm will be fine. Easier to find too! And less likely to collapse on itself under vacuum!
Craig
Thank you for clarification, that will safe my time, I wanted to make another holder with wider hose diameter just for test.
I will try to hold down piece of aluminum 50x50mm and only 50% of that space area is being vacuumed. I will do a test after the glue dries.
I do not even know if -1 bar is enough pressure. My pump is just 3CFM so I assume that I should choose something like 10CFM for faster work.
Hi,
the best possible vacuum is 1 bar, you cant do much better than that.
I use imperial units for pressure, at least for seat of the pants stuff like this. 1 bar is near as dammit 15 lbs/sq.in.
If the vacuum surface is 2 sq inches then the force is 2 x 15 = 30lb force .Easy. Is 30lb force enough....well that's all about what you want it to do.
Craig