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I was wondering how you would control the flow of powder from a container (with a small cylindrical dispenser at the bottom).

The container is filled with powder. As the container drains, less pressure will be exerted on the bottom most powder, affecting the flow rate (at least, I think).

Say I select 32.5 grams and hit a button. What process would you use to deliver this measurement of powder from the nozzle?

  • Would a lasar work?
  • Would there have to be a measurement of the current mass?
  • Would you need to know density?

I also posted this on Quora and got a very nice introductory answer but something more specific could help me. Also, I was given a link to the Weisbach equation, but the contents of the container will be a powder. Probably varying in their size and density as some powders will be finer than others. But in general, how would you solve this?

I know the pharmaceutical industry uses expensive equipment to achieve this, but I am not thinking industrial. They are filling tiny little pill capsules with exact proportions. The focus here is household use, with maybe 15–40 g servings

What I am looking to do is input varying size of serving. 20 g, 22.5 g, 35.5 g serving. Optimally, the system will have an electronic motor component, CPU and a valve that opens/closes with use of the motor...

One of my part time jobs is at McDonalds. We have this cream/milk dispensing machine. You input double-double, and out comes 2 creams for the corresponding cup size. I wonder how those work? The paramount different in systems being those dispense liquids, and we're looking to dispense powder solids.

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    $\begingroup$ A worm drive / feed screw / augur allows an approximation to controlled volume feed. $\endgroup$ – Russell McMahon Aug 25 '15 at 15:53
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Ok, stick with me. I am going to tell you how to do this at home on the cheap and easy, but first lets talk about a few industrial approaches. Because maybe you want to try for something more exciting!

There are several industrial approaches that are used for metering (this is the technical term you are looking for) solids out of container. They range from an Auger or Screw Conveyor to my favorite the Shaking Screw Conveyor

It would be a fun project to build either of those at home, but what you are looking for is a far simpler batch style dispenser. This is accomplished with 2 large valves and a secondary metering vessel. At the bottom of your main storage container there is a valve A, which leads to the metering vessel; at the bottom of this vessel is valve B. To meter out exactly the right amount, size the metering vessel so that it holds the mass you want (i.e., 20 g). All you do is close valve B, open valve A, wait for the metering vessel to fill, close valve A and then open valve B. You will get exactly the same amount every time and you don't need to worry about the flow rate changing as the container empties. all that you need to do is be sure you size the valves large enough so that the solid can fall through them. If its a powder than a 1" valve will work just fine.

This is a boring but exceptionally simple solution. Personally, I would try to build the shaking conveyor.

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    $\begingroup$ Very good for simplicity and accuracy with certain substances, table salt for example. But note that if the substance you are metering has a tendency to stick to itself, like flour or brown sugar, you will run into complications with the substance not falling into the bottom vessel by gravity alone. A simple solution may be this same setup but with an auger or aggravator of some sort to ensure the powder is indeed entering the second vessel. Sounds like a fun little project. Good luck! $\endgroup$ – Alecg_O Aug 25 '15 at 21:34

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