Irrigation systems are designed to transport water to various parts of your lawn, so that you may supply the lawn with water without dragging hoses and sprinklers around yourself. The water in the system must be removed in the winter to keep ice from forming that might split the pipes. When your system is turned back on after a winter break, or after it is first installed, there is sometimes trapped air in the pipes. This creates a terrible noise and is best removed to prevent possible damage.
Pop sprinkler heads off of water irrigation lines that run out into the yard to speed up the velocity of the water running through circuit lines. Look for the screws holding them in place and unscrew them with a screwdriver. The air should flush out of the system within a few minutes.
Turn on the irrigation system at the control panel.
Go the main valves where the irrigation system is hooked up to the main water line. You should see several valves that run to the different circuits of your irrigation system. These are automated so that the system waters various sections of the lawn at separate times. This is needed so that there is enough water pressure to flow out the sprinkler heads.
Manually turn at least two of the circuit valves on. This flushes out the main pipe more quickly by opening up the pipes in front of it, which in turn forces the air out.
Turn off the irrigation system after five minutes of flushing, and then restore the circuit valves to their original position.
Put the sprinkler heads back on the lines.