I'm looking for a practical solution to release a drip of water on command. I'm not too worried about the accuracy of the amount but something around a tenth of a milliliter would be ideal.
I've considered a syringe with some kind of arrangement with a stepper motor but then I'd have to have some way of refilling the syringe on a regular basis (I'm hoping to have a reservoir of about a pint or so).
Then I've thought about the concept of perhaps using an inkjet print head but I can imagine that getting furred up pretty darned quick. Not to mention the hassle of trying to clean out the ink from an existing cartridge.
A tenth millimeter ? You mean 0.1 mm3
What about timing, does that need to be accurate ?
Using a valve (or printer head) is not very accurate for the volume. The amount of water would depend on the pressure of the water.
For an accurate amount, I think you need a syringe. At least that is what has been used for accurate volumes since a long time.
When you have a super large budget, you could use an autosampler, and let the syringe take the water from a bottle.
As far as I know, the autosamplers eject the whole syringe, but perhaps my knowledge is outdated.
I think that your idea to use a stepper motor to make many drops and refill it once in a while is the best option so far.
Hi Peter.
No I definately mean a tenth of a Milli Litre (about a fiftieth of a teaspoonfull.). I think you're right about the syringe being the way to go. I also wanted the control to be really simple. Maybe a solenoid on some kind of ratchet system so that each pulse advances the plunger a small amount. I'll do some playing
Sorry, I was reading that from a beamer image, ha ha, millilitre it is.
To start with something simple, do some tests with just a valve. When the water pressure (the height of water) is about the same, there is about the same pressure at the valve. A microvalve can be used, or maybe just a normal valve.
These are direct acting. Inside is a spring to close it, it pushes a rubber-alike core to the outlet. When activated the core moves towards the inside and opens the outlet. The higher pressure should be connected to the connection on the side.
Allthough it is a weak spring, they open and close pretty fast. http://www.ebay.com/itm/141406897799
A syringe with no-return valves for input and output is a relative simple way to do it using a precise stepper motor, but i don't know how durable is one is used multiple times, i only know about single use ones that tend to fail after some time.
Groundfungus. The peristaltic pump is an inspired idea. The beauty is that it would automatically fill itself. I could still probably create an impeller using a solenoid on a ratchet. This has potential
I've worked with some of the cheap (~$13) Chinese peristaltic pumps before. I think trying to use a solenoid and ratchet might be over complicating it though. Unless you already have these parts and a way to easily assemble them, I think trying to control them with a stepper would be much simpler. You also might want to try using a small fitting at the end as it might make it easier for the drop to drip from the fitting than the tube.
+1 to peristaltic pump + stepper, unless you want to conserve power, in which case
a DC gear motor + encoder driving the pump might be better - a CRS even.
