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Q & A: Making a vacuum on the cheap

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Most recent answer: 10/22/2007
Q:
How can I create a vacuum using household materials that require no electricity? The vessel in which the vacuum is created has to be large enough to float a penny and a feather.
- Braden (age 14)
untington Beach, Ca.
A:
You can make a vacuum in a very small space with a suction cup -- the space between the cup and the smooth surface will be a so-so vacuum. For a larger vessel, such as the one you have in mind, a pump of some kind (or another trick, which I'll describe below) is needed.

A hand-operated vacuum pump works a lot like a bicycle pump. You may have to scout around to see where you can buy one. All that's needed to make one is a tube, a plunger with a handle that makes a good airtight seal, and two one-way valves, one which lets air in, and the other which lets air out, and tubes needed to attach it to your vessel without leaking too much. Bicycle pumps have all of these ingredients, but you'd need to attach the tube going to your vessel to the air intake of the bicycle pump, and this usually is not easy (it's usually along the moving piston, and it's hard to make a good seal on moving stuff). Or you could just by a hand-operated vacuum pump.

The other way to do this is by using a trick. You could heat up the vessel with the end open, plug it up, and then cool it off (be careful not to let thermal shock crack the vessel). Air expands when hot and leaves the vessel, and contracts when cooled off. You will still have air in there, but there will be less than before.

A variation on this trick is to boil water in the vessel with the top open, and then you take it off the heat, wait for the water to stop boiling, and then stopper it up (water vapor may still want to escape, so watch out to make sure you don't inadvertently make a cannon!). Then cooling it off will give perhaps a better vacuum. Freezing the remaining water might give a better vacuum still.

Be careful with leaks! Vacuum grease can help plug these up.

Tom

(published on 10/22/2007)

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