If you have a reasonable pressure, ie mains, there are all manner of solenoid valves available at your local hardware or irrigation shop.If you don't have much pressure it's a lot harder.______Rob
More information required :a) temperature of waterb) pressure across valve when closedc) flow rate through valve when opend) power supply used to operate valve (low voltage 6/12/24DC or mains 110/230AC)
Why is pressure necessary?
5vDC or whatever I can get the arduino to max out at with out using a relay.
Quite often pond pumps are centrifugal pumps which don't always need to be closed when turned off.Turned on they pump water up, once you cut the power gravity will let the water above the pump flow back through the pump into the reservoir.
I've seen a lot of thread on this and other forums where people wanted a cheap low-pressure valve.I have yet to see anyone actually find one. If they did they didn't report the fact.There have been all sorts of methods proposed to bodge something up, but nothing I've seen that's reasonable. One of the problems is that ball valves require a huge amount of torque to turn themOTOH if you are pumping and there is no pressure when you stop then you can just turn off the pump and have a non-return (or check) valve.What's the exact application?______Rob
If you want a low pressure "solenoid valve" then go for a motorised central heating zone valve. These operate from mains AC but more importantly are readily available and reasonably cheap. In fact you should be able to find one at your local scrap dealer for pennies.Alternatively have you considered simply turning off the pump
If anyone has ever heard of such a thing...
I can see at least one problem with this approach, what they call "sticktion".In other words it takes more energy to start something because it's "settled" in one place and the grease, dirt, general friction etc takes effort to overcome. Once it is overcome things run more freely.So the problem is you pump water until it starts moving, then it moves too fast and you have to pump back again. If you pump too much back it may stop and you're back to square one. Don't pump fast enough and the thing runs away, pump too fast and it goes the other way.This assumes that you have feedback and actually know what directing things are pointing. Even if it works perfectly you still need feedback.If the above happens I doubt your pump will be able to move water fast enough to stop it, so the panel (or whatever it is) will slam to the end position.If this is a panel or something with a large surface area then it will be subject to wind loading and once again without feedback you won't know it's moved. By definition the system is well balanced so therefore easily upset by wind, a bird or just about anything.All in all I think you're cruisin' for a bruisin' with this approach, an object sitting on a CV is inherently unstable, once it gets just a tad out of balance it will take off and your system doesn't sound like it will have the response time to correct problems.EDIT: If you just want to follow the sun you can usually do that with a motor, some threaded rod and a nut (for one axis admittedly, double for two). Very cheap.______Rob