A rain sensor is designed to shut down a sprinkler/irrigation system when it rains, thus conserving water.

The pressure vacuum breakers consists of a check device (valve) and an air inlet, which is usually a chamber vented to the atmosphere.

Terms used in articles on backflow testing. Air Gaps– Physical separation between a potable water system and a receiving vessel or source of contamination. Air gap between the outlet of the potable system and the flood level rim of the receiving vessel or any source of contamination must be at least twice as large as the diameter