Most sprinkler solenoid valves run off of 24VAC (VAC: Voltage, AC) and have an amperage requirement of ~200mA. These solenoids are quite common, and can be found in any hardware store. 

RainMachine will not work with "industrial" or "commercial grade" valves, as they tend to use over 1A or more of current draw, and the RainMachine only can supply up to 750mA. This will result in a overcurrent, and the device will be unable to activate your zones/valves.