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Automated fluid dropper Answered

Hi,

I want to release droplets of water one-by-one on command, and have been doing some research on how to do that, but I'm wondering if anyone has some other ideas or has heard of a ready-made solution.

So far I have come across:


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-peristaltic pumps with really low flow rates, like the one here

http://aptinstruments.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=AI&Product_Code=SP100VO&Category_Code=

It goes down to 0.09 ml/minute, which should be small enough. I can selectively turn the pump on and off, feeding water to a small tube or dropper end, producing the water drops. These are pretty expensive, the cheapest one I've seen is around $60.


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-DIY systems like the one pictured here
with a solenoid opening and closing a safety pin on a tube.

http://www.maggiecarsonromano.com/index.php?/projects/what-made-the-wound-wound-the-thread/

Maybe I could tune the distance of the solenoid so it just opens the pin a tiny amount, and a drop or so is allowed through.


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-or I could use a more typical water pump, attach it to something with a really small aperture. I could turn the pump on and off. I have a hard time picturing drop-by-drop control with this, I might be able to release very small amounts, and maybe some 2nd reservoir between the motor and dropper could be designed to aid this.


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Is there a ready-made solution to what I'm trying to do? If I just get a regular water pump what should I look for? Ideally I'd like to get a pump that's as quiet as possible, too.

Thanks bros.
Josh
 

Discussions

Simplest thing I can think of is a syringe with a worm screw pushing down on the plunger, rather like a c-clamp. A gearmotor or servo might run slow enough that you could just let it run, or with a very simple DC motor controller. Something like this.

Could one use a screw type mechanism to "move" the water (the screw being on the inside of a tube like enclosure) where it would lift only a drop or so of fluid in each "turn"?

Archimedes' screw! I don't know how scalable that is, since they're generally used to transfer large volumes of water, but I like the idea. Something like a length of all-thread in a close-fitting copper tube might work.

Archimedes_screw.JPG

yes, I was thinking of a less angled screw for moving maybe smaller amounts (if the tube was also small.

And an Archimedes' screw typically has very broad threads compared to the central shaft size, because they're trying to move as much water as possible. Threaded rod has very narrow threads relative to the shaft, so it would be much slower by nature.

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Pncgs

7 years ago

You might consider using a syringe pump and a controller. Google "syringe pump" for ideas.

The peristaltic is probably the most sensible method. I've seen small pumps for much less than 60 USD on Ebay.

Steve

a peristaltic pump should be pretty easy to make DIY like anyway. all you need is a motor, an oblong (or at least a circle with a bump) piece of material, and a housing. they work by turning the oblong piece within a circular housing. as the oblong piece comes around to the part of the housing that's closer to the tube, it pinches the tube and pushes the liquid through the tube which in turn sucks more fluid up to fill in the gap.

At what rate?
Does the rate vary? And if so...
What's the minimum rate?
What's the maximum rate?

i want to be able to trigger a single drop and not have it give any more drops or any less (no drops). that's the priority. what was your motivation for asking about min/max rate?

well let's say i want to be able to trigger a drop almost instantaneously. say 1 second.

let's also assume that i when i turn the pump on/off, it starts at the desired rate (or stops) almost instantaneously.

a drop of water is about 0.05 mL, so doing the math I would need a pump rated for at least 3mL/min.

i may not need to remotely change the rate of the pump, or change it mid-operation, but i will need to be able to tune it to the desired rate prior to operation to get that one drop. that one drop is what i'm after.

i'm planning on probably using an arduino to turn pump power on and off, unless there is a pump that offers better control. it seems plausible to me (though i've never worked with pumps so i don't really know what i'm talking about) that one second is still too fast to expect the pump to get up to desired speed after flipping it on, with the accuracy required for this application. maybe i would need 10 seconds at a lower rate for a single drop.

do you kind of get what i'm asking? i guess it's more big-picture. i'm looking at these peristaltic pumps because they're the only ones i see operating at this low volume, but i keep reading about them being used mainly in applications with corrosive chemicals, etc…is there another kind of pump i should be looking at? where do i find information about tiny pumps, i'm just kind of at a loss.

i should also add that i've seen youtube videos of people with a syringe in a little custom-built stepper motor frame thing that pushes the plunger in when it steps. i could do that, but then i would need to fabricate that frame, which i don't really want to do. they're big and ugly and that would be a project in itself.