Pumps

http://nxtwave.tripod.com/suctionpump/index.html shows some details of a 
experimental suction based pump toy that kids might be interested in. Make
the toy first and see if you can scale it up!
Brian White
 The links below show more develloped pumps

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internet glossary of pumps
http://www.animatedsoftware.com/elearning/All%20About%20Pumps/glossary/aap_glossary.html
Pulser pump home http://nxtwave.tripod.com/gaiatech/pulser/index.htm