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How Do Pneumatic Tubes Work?

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The Internet has been called a series of tubes. But long before email, people sent messages across cities through networks of pneumatic tubes. Learn how they work!

Learn more at HowStuffWorks.com:
http://electronics.howstuffworks.com/everyday-tech/pneumatic-tubes.htm

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The Internet has been referred to as a series of tubes. But long before email, people transmitted messages rapidly across cities through networks of pneumatic tubes. These are pipelines that use air pressure to propel canisters from point A to point B. You can still see them at the drive-through windows of some banks and pharmacies.

But when I say “long before email,” I don’t mean the ‘way groovy Sixties, man,’ or even the ‘rip-roarin Twenties.’ I’m talking about the mid-1800s... which I don’t have a specific accent for.

The idea of using pressurized gas to produce mechanical motion goes all the way back to a Ptolemaic Greek mathematician called Hero of Alexandria. But the first practical application of the concept sped mail and telegrams through London starting in the 1850s.

By 1886, London had 34 miles of mail tubes underneath the city transmitting 32,000 messages a day at up to 51 miles per hour.

Cities like New York, Boston, Paris, Berlin, and Vienna had similar systems by the turn of the century, though the world wars and the growing automobile industry shut most of them down by the 1950s.

The technology is still in use today to transport materials through manufacturing plants, medical samples through hospitals, and your bank deposit slips to you.

“But how??” you demand of your computer screen. It’s inanimate and I’m prerecorded, but I’ve got the answer for you anyway.

These pneumatic systems start with an airtight tube with sealable hatches at either end. You put your Thing What Needs Transporting in a canister that’s smaller than the tube, but has flexible skirts on either end that can form to the interior edges of the tube.

You put your canister in a hatch and press the “go” button.

The button activates a motor at the other end of the tube, which opens a vent and turns a fan. The fan drives particles of air from the tube out through the vent and into the wild blue yonder. Thus creating a difference in the density of the air in front of the canister and behind it.

The denser air behind the canister pushes it to its destination. A trap door closes behind the canister, the motor stops (breaking the partial vacuum created in the tube by the fan), and your buddy can open the hatch and take the canister.

It’s basically the same thing that happens when you drink through a straw. Your suction creates an area of low pressure at the top of the straw. The higher-pressure liquid at the bottom pushes a sip up into your face.

Of course, that’s the simple version. Complex pneumatic systems may have dozens of branching tubes containing switches, and transfer points that house extra fans.

By using computer systems to carefully regulate the fans and thus the air pressure, even delicate lab samples can arrive safely.

SOURCES:

http://lapsedhistorian.com/get-blower-londons-forgotten-pneumatic-messaging-tubes/

http://med.stanford.edu/news/all-news/2010/01/gone-with-the-wind-tubes-are-whisking-samples-across-hospital.html#.html

http://electronics.howstuffworks.com/everyday-tech/pneumatic-tubes.htm/printable

http://home.howstuffworks.com/vacuum-cleaner.htm

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