In a lawn irrigation system, where must a valve not be installed relative to an atmospheric vacuum breaker?

In a lawn irrigation system, it is crucial to ensure that the atmospheric vacuum breaker functions properly to prevent backflow and contamination of the potable water supply. The correct placement of valves in relation to the atmospheric vacuum breaker is essential to maintain its efficacy.

Placing a valve downstream from an atmospheric vacuum breaker is not permissible because, if closed, it would create a situation where a negative pressure could develop in the irrigation system. This negative pressure might draw water back toward the vacuum breaker, defeating its purpose and potentially allowing contaminated water to flow back into the clean water supply.

When the valve is installed upstream, parallel, or adjacent to the atmospheric vacuum breaker, it does not interfere with the vacuum breaker’s function. Upstream placement ensures that the vacuum breaker can effectively prevent any siphoning action into the clean water supply, while parallel and adjacent placements do not create a risk of negative pressure affecting the vacuum breaker’s operation.

Thus, the requirement to avoid placing a valve downstream is important for maintaining the safety and integrity of the irrigation system.