12V DC Solenoid Water Air Valve Switch  – 1/2″ controls the flow of fluid (liquid or air) and acts as a valve between high-pressure fluid! This liquid valve would make a great addition to your robotic gardening project. There are two ½” (Nominal NPT) outlets. When a 12V DC supply is applied to the two terminals, the valve opens and water can push through.
 
The valve works with the solenoid coil which operates electronically with DC 12 volt supply. As it is a normally closed assembly, it opens the flow of fluids as soon as it is powered ON and stops/blocks the flow when the supply voltage removed.