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I want to make a device that can control a small solenoid valve for dispensing fluids. Basically a circuit which powers on and off the solenoid at different times to allow the fluid to flow. The fluids will be gravity fed so very little pressure is needed. Most of the solenoid valves that I have found are like 100 dollars or more which is way too expensive for this project.

Does anyone know if there are any small inexpensive solenoids, or something similar, that would do what I want? I'd like the flow rate to be about 1 ounce per 5 seconds or somewhere around there but I can reduce the flow if it's more than that.

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I once was looking for a similar thing and came up with following low cost (< 10 EUR) solution, that requires however some handicraft:

  • Plant watering valve (normally for manual operation; e.g. Gardena, see picture; < 4 EUR) operated by
  • a cheap servo (normally used for RC models; < 5 EUR)

Gardena valve

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  • \$\begingroup\$ How much torque must the hobby servo produce, to be able to rotate the control knob? Would you recall what servo you used for this? +1 for unconventional and innovative solution, by the way. \$\endgroup\$ – Anindo Ghosh May 30 '13 at 17:00
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It looks like Sparkfun has a pretty cheap option for solenoid valves. There is only the one size, but at $8 it meets the cheap requirement. It does require 3 psi to operate which may not meet your gravity fed requirement.

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Pneuaire has a selection as well. I've purchased their low watt gas solenoids, and they seem to work. (I've only played around with them, and haven't subjected them to any real use.)

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Clippard has a good selection of solenoid valves. Their line of inexpensive valves is called mouse valves. They cost on the order of $25. I've been using them for years.

Clippard makes other types of pneumatic hardware too: cylinders, regulators, gauges, manifolds, fittings, etc.

Here are a few more manufacturers that may be instrumental for building pneumatics: Beswick Engineering, Norgren.

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Go to the trash dump and get a perfectly good small solenoid valve free. It will be on a discarded refrigerator or dishwasher. Chances are, you can run across such an appliance in an alley if you stay alert, in which case you offer to haul off the junk as a favor to the owner (be careful: don't violate a local ordinance against "Dumpster Diving"==get the owner's blessing, first. If you go to a SALVAGE YARD, they will want to SELL you the valve; however, a lot depends on your gift of gab. AVOID "Moonlight Requisitioning:" it will NOT save you money if you have to make BAIL!

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Windshield wiper fluid pump things from cars are very cheap and plentiful. Lots of them, new and used, on ebay for you to try. Not sure how accurate they'd be, but they've worked well for me when watering plants.

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