# Talk:Vacuum coffee maker

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## Merge

It's obvious the two articles are the same (or were at one point). One should be a redirect to the other, and I personally don't care which way. Gentgeen 06:45, 18 October 2006 (UTC)

## Siphon operation: pushes, doesn’t “suck”

Note that siphons push fluids (fluids are under pressure) – they don’t “suck”. This is a very frequently confused point in siphons generally and these coffee makers specifically, so in this edit I’ve given a relatively detailed explanation of how pressure differences push the water through the maker. Hope this helps!

—Nils von Barth (nbarth) (talk) 04:16, 24 December 2011 (UTC)

It isn't a siphon operation. By definition of siphon, a bent tube is involved to draw the liquid uphill.

If the lower pot was not sealed from ambient atmosphere, it would be a gravity-feed configuration.

Instead, the lower pot is sealed and the only entry/exit of material is through the center tube to the upper chamber. Heat is used to evacuate the lower chamber by increasing the pressure, forcing the liquid out. When cooled, the pressure decreases (i.e. "vacuum is created"), which draws liquid in through the tube.

This is why this apparatus is called a "vacuum" device instead of a "siphon" device.

Windsor (talk) 17:08, 30 December 2011 (UTC)

I'll preface this by stating that where I say vacuum I speak of a partial vacuum, see Suction.

The operation of this device most definitely incorporates both a siphon and a vacuum cycle. The device does this in two separate stages, the heating of liquid where a siphon is in effect and the cooling of gases where a vacuum is in effect.

In the first stage, liquid is heated in a flask which is sealed except for a tube to a separate container. The atmospheric pressure increases in the flask as the heat causes expansion of the liquid and gases. The increase in pressure pushes the liquid through the tube into the separate container. This demonstrates a siphoning action, the liquid is pushed by pressure from the flask into the container.

In the second stage, heat is removed from the flask and the liquid returns from the container into the flask. Because many siphon/vacuum coffee makers use a configuration where the flask is below the container it is easy to believe that the device is relying on gravity alone for the second stage, where the liquid returns into the flask, but it is clear that a vacuum is at work when observing a "balancing siphon coffee maker" (it can be found on YouTube). Once the flask has emptied of liquid, the remaining gases cool down and create a vacuum. In the balancing siphon coffee maker it can be seen that a siphon is not at work as once the flask is empty it is located higher than the liquid in the container and a siphon would not work in this configuration. Therefore, a vacuum is drawing the liquid back into the flask. Further evidence of a vacuum is that, in glass siphon/vacuum coffee makers, once the liquid from the second container is restituted into the originating flask air can be observed to be sucked in, filling the vacuum left by escaped water vapour.

Some points to consider. If the top container is filled with liquid when it is already placed on top of the empty flask (which is sealed), only a minute amount of water will drop down. The flask will not even fill with water to the base of transfer tube, the filter inhibits the passage of air and water further adding to the argument that a vacuum is sucking the liquid back in the second stage. The receiving container is unsealed and therefore the atmospheric pressure within it remains unchanged throughout the process, the only two forces that can be at work to return the liquid to the originating flask are gravity and/or a vacuum as the container has no extra pressure with which to push the liquid back. The balancing siphon coffee maker is evidence that a vacuum is at work. In a wired.com review, the author states that "Half the time, the coffee wouldn't drop down into the lower chamber after I took it off the heat..." This may indicate that where something went wrong in the process a sufficient vacuum was not formed to draw the liquid back into the flask as theories refuting a vacuum should have seen the liquid return irrespectively. — Preceding unsigned comment added by Zarbatron (talkcontribs) 23:32, 28 March 2013 (UTC)