The principle of a vacuum coffee maker is to heat water in the lower vessel of the brewer until expansion forces the contents through a narrow tube into an upper vessel containing the coffee grounds. When the lower vessel has more or less emptied itself and enough time has elapsed, the heat is removed and the resulting vacuum will draw the brewed coffee through a strainer back into the lower chamber from which it can be decanted. The device must usually be taken apart to pour out the coffee.
An early variation of this principle is called a balance siphon. This implementation has the two chambers arranged side by side on a balance-like device, with a counterweight attached to the heated chamber. Once the vapor has forced the hot water out, the counterweight activates a spring-loaded snuffer which smothers the flame and allows the initial chamber to cool down thus creating a vacuum and causing the brewed coffee to seep in.