Lawn Sprinkler Troubleshooting Question About Airating A Lawn Sprinkler System?

Question about airating a lawn sprinkler system? - lawn sprinkler troubleshooting

I mean airating irrigation system. What I know is the valve that your airline in which there are two ports for air. What each of them? That is the goal of the CAP, which is placed on the tap or the purpose of this valve.