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Electromagnetic Valve

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LiquidOrb24

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I I'm sort of an idiot when it comes to electromagnetics (then again who does understand that stuff) and I'm planning on making a automated drink mixer with 10 programmable drinks where I will be using a microcontroller to open up any of the 10 valves for each drink for a certain amount of time to get the drink ratio just right...

The valve itself I was thinking of having a solenoid around an iron rod with at rubber stopper at bottom and a spring on top of it to press it down. When a current flows through it the magnetic field it produces pushes the rod up agaist the spring allowing the drink to pour into the glass for the given time I assign in the microcontroller. However I have no idea how many turns I would need and how much current will be needed to lift an iron rod of about 2 inches enough against a spring to open up the valve, and if that much current can flow through the IC's I will have.

If anyone has any ideas of the power/lift ratio for a solenoid is or how I might be able to accomplish this task that would be greatly appreciated.
 
I wouldn't try to home brew a liquid solenoid, especially one for human consumption. Making something that is well sealed against leakage outside the line as well as past the valve when it's off is really hard. Then ensuring the materials will not contaminate the liquid (like iron will, for example) is the other big issue.

There are plenty of great food-safe liquid solenoids out there anyways.
 
Proof of concept might be better achieved using a a ready made solenoid valve such as those found in domestic automatic washing machines. These can be either bought or salvaged and should pose no problems after a thorough clean up for use with alcoholic beverages.
 
Keep in mind that the fluid flow rate thru the valve will be somewhat dependent on the pressure available to push the fluid thru the valve. If you are planning on using gravity then the level of fluid in the container might govern the pressure therefore the flow rate. That might or might not affect what you are doing.

Regarding solenoid valves - some are pilot operated and require an amount of pressure to operate them. Some won't seal leak tight without enough pressure differential. There are many other things about solenoid valves that could trip you up aside from what's already been mentioned.

Some other thoughts --

Use flexible tubing and a pinch type valve

Consider low pressure air or gas to push the fluid/components from a storage container. I've seen low cost auto type air or vacuum solenoids that might be easily adapted. Just remember that compressed gas in a glass or plastic bottle can be dangerous.
 
solenoid

Drinks are corrossive substances and can react with ordinary materials( eg., you can etch a PCB in coke, given enough time!)
Electromagnetics are simple enough, as far as they are industrial and not 'Food Grade'.
The 'pinch cock' method is tricky, not to mention wasted current consumption: it has to overcome the liquid inertia as well as the pipe/tube elasticity. Solenoids ARE power hungry!
The simple and probably cheap solenoids come out of Water Filter-dispencers, Coffe/soft drink vending machines, and are designed for liquids under pressure, temperature and chemical extremes.

Alternative to this and for experimentation, you can dismantle DC or AC relays rated at at least 20A contact current capacity, and use the coil. You have to use soft iron for better performance. ( nails are Mild steel) and retain some permanent magnetism ). The Relay coil will be found sitting around one of these soft iron cores. AC single /#phase contactors are the best bet. having awesome pulling power.
For the valve mechanism, a steel ball (Teflon coated) freely seated on a rubber O ring by gravity inside a vertical Corning glass/ nonmagnetic chrome steel tube would be an ideal construction. The relay coil will surround this tube such that the ball will be lifted up due to the magnetic force field.

stevez' second option is fairly easy, and i feel the best method. CO2 gas or even an electric Tyre inflator, at low pressuere can be used to eject the fluid through a siphon tube. You neednt concern yourself about 'food grade, acid resistant materials' at all!

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Thanks alot guys you gave me a lot to think about I will consider all possibilities and think things through and redesign my valve

Thanks for the help guys.
 
You may want to look up pstolic pumps (I think that is how it is spelled!) They use a soft tubing, and a cam system to move liquid through the tubing. IV pumps use them. They can measure very accurately.
Also, consider a small submersible pump, although the output changes with amount of head, so this could be a bit tricky to use.
I have come across a drink dispenser using the pinch system with soft tubing, somewhere on the net. Ah, here you go, they even tell you where they got the solenoids.https://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2005/vhl4/juicer_webpage/index.htm
Ah, no, that is not the one with the pinched hoses, they use another method. Still worth looking at, as their project is similar to yours.

Great idea,
Regards,
Robert
 
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