What is the critical component of an atmospheric type vacuum breaker that is subject to failure?

The air inlet valve is the critical component of an atmospheric type vacuum breaker that is subject to failure because its primary function is to allow air to enter the system when there is a negative pressure, which prevents the formation of a vacuum. If the air inlet valve fails, it may not open when needed, potentially leading to dangerous backflow conditions. This is essential for maintaining proper drainage and preventing the siphoning of contaminated water into the potable water supply. A malfunction in this component can result in significant issues, including the risk of contamination.

The other components, while important in their own right, do not pose the same level of risk directly related to vacuum conditions as the air inlet valve does. The pressure relief valve is designed to alleviate excess pressure, the check valve prevents backflow, and the shutoff valve controls the flow within pipes, but they do not operate specifically to counteract vacuums in the same critical way as the air inlet valve.