I'm looking at googles mocktails maker. And it puts 2 holes in a container. 1 hole is connected to a pump that will take water out and the other connects to a backflow prevention valve that only allows air in and not liquid.

What is the point of having that valve? It doesn't connect to anything. Also when I test it with and without having that valve the water does the exact same thing.

Reference: https://github.com/deeplocal/mocktailsmixer#step-19-attach-tubing-and-check-valve

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EDIT: Does it have to do with keeping the container pressurized? Why would I need to have a constant pressure if the pump doesn't require it.


1 Answer 1


yes it is just to maintain the pressure in the container at the same level as atmosphere.

Many small pumps malfunction when the source reservoir has vacuum built up in it.

Even simple bottle water dispensers have check valves that lets air replace used water and break the vacuum.

Especially unable to handle the negative head are peristaltic pumps, which function by a rotary triangle of wheels squeezing the water in a tube forward, because of a random bubble of air trapped in the tube between the wheels.

  • $\begingroup$ Those are called peristaltic pumps $\endgroup$ Dec 20, 2018 at 17:47
  • $\begingroup$ @JonathanRSwift, fancy name. Our own body has a similar circulation system built into our veins. They are equipped with one-way check valves directing the blood back to our heart, when the vein is squeezed by an adjacent muscle unintentionally aiding in our blood circulation. $\endgroup$
    – kamran
    Dec 21, 2018 at 0:55

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