Most new automatic sprinkler systems use digital read-out clocks. The system operates from a central water supply line. This pipe, which is usually made of white polyvinyl chloride, commonly called PVC, runs from your water service line to your system's zone valves. Zone valves are solenoid valves that allow water to flow from the system's main line, through smaller lines, and out sprinkler heads. Most systems have several zones, each controlled by one or more zone valves.
Lateral lines lead from the zone valves to the sprinkler heads.
Lateral lines are usually made of black polyethylene pipe, or poly-pipe. Permission is hereby given to duplicate this Plant talk Colorado TM script as is if credit is given to the sources.