What happens if the critical level marking is not shown on a vacuum breaker?

If the critical level marking is not shown on a vacuum breaker, the bottom of the device is taken as the critical level. This means that the vacuum breaker is assumed to be designed for operation at that level, and it is crucial for the correct functioning of the device to avoid backflow and potential contamination of the potable water supply.

In plumbing systems, the critical level is the point at which the water in the piping system can potentially siphon back into the system, leading to contamination. By defaulting to the bottom of the device as the critical level, this guideline ensures that the device is installed at an appropriate height above the highest flood level of the fixture it serves. It is essential for maintaining the functionality of the vacuum breaker, which is designed to prevent backflow and maintain a separation between non-potable water and the potable water supply.

If a vacuum breaker operates without a defined critical level marking, relying on the lower edge of the device helps ensure that there is a measure of protection against siphoning events. Proper installation based on manufacturer instructions—including critical level markings—is essential for compliance with plumbing codes and for ensuring safety in water supply systems.