I'm working on a computer-controlled indoor waterfall. One of the requirements is to be able to change the water pressure via computer interface. I've googled all day long and can't seem to find a valve that can be controlled via computer. Anybody happen to know of such a device and where I could find one?
If you're in the US, try a 24 V DC solenoid valve from McMaster-Carr: http://www.mcmaster.com/#solenoid-valves/=8to0so
To control it from a computer, you'll also need a 5 V relay that can be controlled by something like an Arduino and a 24 V power supply. You might be able to find a solenoid valve with a low-voltage relay built in, but I've not seen one before.
I don't think that ON/OFF valves are the way to go for your project since that will hardly give you precise and fast control of water jets amplitude for your fountain.
DC water pumps like Attwood V500 can be easily controlled via PWM, and 0-100% can define the height of each independent fountain water jet amplitude. Interfacing these 16 water pumps can be seen here and especially here.
Of course, you don't have to complicate and use FPGA. You can just use some simple microcontroller board like Arduino. It can run fountain on it's own (like changing some predefined patterns), or it can be controlled by some PC application (like audio spectrum analysis via custom WinAmp plugin).
Slightly different principle but with similar effect (although less controllable and less powerful) can be made using these micro valves. Which one to choose depends on your specific application.
How about building your own?! If you have the time and inclination. It may be cheaper and you could learn a lot of useful stuff in the process. Take a mini servo motor, couple it with your inlet pipe and you have a rudimentary but workable valve! Of course you may need to extend the servo motors fins with custom cut PVC portions that match your pipe, but that is not really difficult. You'll need a micro controller or something like an Arduino for precise control of the servo.
Excuse me – I didn't see that you needed variable water flow. Perhaps you could pulse this, but I do not believe it is what you want. Anyway:
I just bought a bunch of "Electric Solenoid Water Valves" from Seeedstudio Depot: http://www.seeedstudio.com/depot/electric-solenoid-valve-p-636.html?cPath=119_121
They work well.
I am doing something similar, except connecting tanks at different levels together. Whilst I could have used a solenoid valve to control the valve, I do not want to consume power the whole time the valve is open, which could be days or weeks.
I am fabricating a small DC motor to drive the valve for on to off, and it will use optical sensors to close the feedback loop. If you were to use a flow sensor and an arduino, you could open and close the valve to any point.
When I am finished, I could send you a photo, and instructions on doing your own.