The document discusses the importance of air valves in wastewater systems. It explains that force mains need to release trapped air to prevent damage from pressure build up. There are four main types of valves that can release air or break vacuums: air-release valves, vacuum breakers, air-vacs, and combination valves. These valves need to be installed at high points and changes in elevation along force mains. Proper maintenance of air valves is also important to prevent clogs or build up that could impair their function.