Pressure transients wreak very extensive damages to water and wastewater transmission systems. Until recent years, most of the concern related to pressure transient damages was focused on the obvious extreme events of pipe burst or collapse that result in major spills or flooding. But, there are many damages, far more widespread and often more dangerous, that are less obvious and attract less attention. Pressure transients cause cracks and unseen small breaks in buried pipelines, pipe fittings,

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... and accessories. They cause joints to fracture or to come apart, they cause damage to seals and gaskets or cause them to shift out of their sealing positions. These damages result in leakage and in contaminant intrusion and their consequent economic, environmental, and public health repercussions. Municipal and industrial wastewater leaking from transmission pipeline and force main systems damaged by pressure transients infiltrate, pollute, and contaminate ground and surface water, soil and the environment in which they pass, becoming dangerous health and environmental hazards and nuisances, spreading odor and providing havens for mosquitoes, flies, and other disease spreading insects. Water and soil polluted and contaminated by leaking wastewater can bring to pathogen and toxin intrusion into drinking water systems. All these repercussions of pressure transients have come, more and more, into the limelight in the past few years, and great efforts are being made to control them. The advantages of air valves as efficient and cost effective tools for the control of both, pressure transients, and their dangerous consequences, are often overlooked or unfamiliar. Modern, well designed, often innovative air valves, with the help of modern design tools, such as air valve sizing, location, and specification software and advanced transient analysis software, can control and dampen transients and eliminate or limit their damages.