Vacum system usage

[petek]

If you're interested in calculating vacuum pressure vs. vacuum cup size vs. lifting capacity, there's some basic info here.

Keep in mind that vacuum pickup cups are very sensitive to leaks - it doesn't take a big one to cause a loss of attachment. Also, if you use place the vacuum generator far from the cup(s), and use small-bore tubing, it will take a loooong time to attain or release vacuum out at the cup. Finally, if you have multiple cups connected to one vacuum generator, a leak at one cup will affect the others unless you play games with restrictions in the lines (which will slow down the vacuum flow even more).

My advise to anyone who hasn't used vacuum before: don't expect vacuum to behave anything like compressed air, and remember that a perfect vacuum is only 14.7 psi (and you'll never get perfection).

[ngreen]

Originally Posted by petek

and remember that a perfect vacuum is only 14.7 psi (and you'll never get perfection).

This remind me of a something my transport (fluid dynamic) teacher told us once. When he got out of college he went to work in St. Louis in a plant right off the Mississippi. There was a recent fire at the plant and the fire pump truck tried to use water from the river but were unable to. One of my teachers first job was to figure out what went wrong. Aparently the pump truck had tossed a hose down into the Mississippi expecting to be able to pump it up to put out the fire, but the water was 90 feet below the pump truck. Since a perfect pump could only draw 33.9 feet of water (or 760 mm Hg, 14.7 psi, etc.) the pump truck had no chance of pump 90 feet up to the fire.

[BrianR]

Just a note... We experimented with the suction cup, and found that it left something to be wanted. One of our mentors works with suction to some degree, and this particular cup is perfect for lifting solid object, such as a sheet of glass. We noticed that you have to make sure to press down hard on the tube to make it stick, but after that it still works fine. My only concern is how these tubes will interact with the suction cup once they have gone through a variety of matches and have had a chance to accumulate alot of dirt.

Currently, our team has split, and we are designing two lifting mechanisms, one with suction and one without. We're going to mock them up and see which one is more efficient/effective.