I want to use arduino to control a set (e.g. 12) of small air valves that would be submerged in a tank of water.
The idea is to control the release of air bubbles via an arduino.
I have no experience with pneumatic systems and I was wondering if anyone can point me in the right direction for suitable submersible remote controllable air valves?
Try to find them surplus: the prices on new ones are shocking. Even in this Robotic Age, there's still a lot of custom industrial equipment being made that uses pneumatics to push and clamp things. But now they're using lots of solenoids valves because they're computer-controllable.
If possible, put the valves outside the tank, and run hoses into it. The cost of submersible valves is probably going to be a lot higher. Plus, your odds of finding used ones probably go up if you're looking for non-submersible ones.
Oops: a third suggestion. Many years ago, I worked on a system for controlling the air/fuel ratio in trucks. The hardware designer picked a low-cost 12V valve that had been designed for sprinkler controls (I think). It was a spring-loaded solenoid, not a motor turning a "tap"-type valve. We PWMed it with 10Hz to vary the amount of extra air being let into the engine to adjust the mixture. It might not work for you, because we were basically using it to make a "controlled manifold vacuum leak", while you'll have to use a higher pressure to force air into the water tank. But it's worth checking into. Unfortunately, I can't remember any manufacturer or model info for you. But it was a cylinder, about 1.25" diameter and 1.5-2" tall, with a blockish piece on top that had the tapped holes for the inlet and outlet fittings on it. Try googling for "sprinkler solenoid valve".
Running tubes into the tank is totally doable. I also forgot to mention that I need to figure out a small and hopefully quiet air compressor system if I am going pneumatic.
Depending on how much air you need and how deeply you need the bubbles to be released, you could also use aquarium air bubblers. They're pretty cheap and quite quiet, and can be simply turned on and off with a relay/triac.
If your tank is very deep, remember that the pressure required to push air into the tank is dependent on the height of the water column above the end of the tube.
Most off-the-shelf air compressors are pretty loud, how quiet do you need it to be?
If the air volume is low, you could use aquarium pumps. They're quiet and readily available. In fact, it might work to hack them: replace the motor with a DC unit you could speed-control to adjust the volume, instead of messing with valves.
Those nitinol air valves do look interesting. I never got involved with the stuff because I never had a use for it: it's relatively slow-moving, and my recollection is that it takes quite a bit of power per ounce of force. I've also been suspicious of its durability, but that's based entirely on a "common sense" feeling that constantly heating and cooling metal must invariably lead to fatigue. It could well be that there's something about that alloy that minimizes the effect. You should do some research into the experience of people who've used it heavily: by now, there should be info from hobby robotics folks who've cycled actuators tens of thousands of times. Also, make sure the valve can change settings as fast as you need it to.
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I recently spoke with a friend of mine, who is an engineer who constructs spirit production facilities. They use extensively hydraulics there, as any electrical spark can lead to fire. The pressurised lines are long and are used to control things and the electrically controlled valves are outside of the building.