Now_What - 5/15/2016 20:40

You need the pressure relief because the air compresses as the pipe fills with water and you can end up with some serious pressure much greater than what you are pumping into the system.

I didn't believe it at first I thought there was no way there could be that much pressure created by compressing air and thought the less risers there were the better until I saw a pipe blown apart at our neighbors by compressed air from filling the pipe.