When must a bag filter be replaced according to operational guidelines?

A bag filter must be replaced when the differential pressure exceeds 20 psid. This threshold is significant because it indicates that the filter is becoming saturated and may no longer be effective at trapping contaminants. When pressure increases beyond this point, it can lead to reduced flow rates and potential bypassing of unfiltered water or fuel, which defeats the purpose of the filtration system.

The operational guidelines are designed to ensure optimal performance and longevity of the filtering system. Operating beyond the specified differential pressure not only risks system efficiency but also can cause stress on the filter media, leading to potential failure. Maintaining the filter according to these parameters is crucial for effective water and fuel systems maintenance.

The other options suggest lower thresholds or unnecessary replacement frequencies that do not align with standard practices for ensuring filter effectiveness and reliability. Proper education on these guidelines aids personnel in maintaining equipment properly and preventing operational issues.