In pressurized tanks, when is the signal initiated for water level supervisory devices?

The signal for water level supervisory devices in pressurized tanks is typically initiated when the water level falls or rises by 3 inches. This 3-inch threshold is significant because it provides a reliable measure to alert monitoring systems about potential issues within the tank, such as leaks, overflows, or other irregularities in water level. By setting this standard, it ensures that the supervisory devices maintain an adequate response time to any significant changes in the tank's water levels, which could affect the system's performance and safety.

Monitoring devices that alert on a smaller change, like 2 inches or a larger change, like 6 inches, may not effectively respond to early indications of problems. The 3-inch level serves as a balanced approach that helps maintain system integrity while preventing unnecessary alarms caused by minor fluctuations.