An ink supply for an ink-jet printer is provided with a main reservoir, which is typically maintained at ambient pressure. The main reservoir is coupled to a variable volume chamber via a one-way valve which allows the flow of ink from the reservoir to the chamber and prevents the flow of ink from...http://www.google.es/patents/US5844579?utm_source=gb-gplus-sharePatente US5844579 - Out-of-ink sensing system for an ink-jet printer
