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I am making a "bar bot" and I am trying to figure out a way to dispense soda without it going flat. I am using a bunch of peristaltic pumps:

pump gif

Which luckily remain sealed at rest. I was thinking of drilling a hole in my soda cap and hot gluing a pipe barb so I could pump soda from the sealed container. I realize that without replacing the dispensed liquid with an equal amount of air, this will slowly create a vacuum in the bottle which will become a problem eventually (I imagine the bottle will start collapsing in on itself). I think I should be solving an issue like this with some sort of valve, but what type?

I am looking for something very small and cheap that will remain sealed at rest (don't want the soda going flat). I only want the valve to open when the pressure in the bottle drops below atmospheric. MOST importantly I am looking for a valve that does this automatically. If I need to fiddle with it manually, I would just uncap the bottle myself every once in a while. There is a valve that can do this mechanically no?

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  • $\begingroup$ You need to keep it pressurised, and ideally cold. Having it just at atmospheric pressure is not enough to keep it from going flat. $\endgroup$
    – Jonathan R Swift
    Jul 13 '20 at 10:01
  • $\begingroup$ Sucking the liquid out of a sealed bottle will cause the gas to come out of solution to fill the void and make it go flat extra quick. $\endgroup$
    – Transistor
    Jul 13 '20 at 11:26
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Add air or C02, using a pump,to keep the contents above atmospheric pressure or at the pressure of the soda bottle. Not sure what that is as I have never measured it, but some seem to be significant and they can push out quite a bit of the contents.

That means you will need two barbs to the lid. Consider making special lids - perhaps out of brass or stainless so that the pipe connections are more reliable.

This, of course, means that you only have to control delivery, just a simple delivery valve may do.

Also it will be a good idea to have oneway valves on the air (C02) supply to prevent backfeeding from any soda bottle into the one being used. A valve to allow changing the soda bottle would be a good addition.

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Without storing the soda in bags, I think you will struggle to find a solution that works better or even at a lower cost than the syrup & carbonated commercial solution. Mechanical check valves are not going to work well enough at the very low pressures we'll find here. and solenoids just complicate a system that I assume you are trying to keep simple to avoid the commercial solution.

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Spring-loaded Gravity-flap valves should work as monodirectional pressure stabilisers at an air intake. I don't know how this would affect shelf life of fluid being distributed but it's an idea at least

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  • $\begingroup$ I suggest you elaborate on your response. Currently the response is more like a comment. $\endgroup$
    – Mahendra Gunawardena
    Jul 28 '20 at 4:01

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