What commonly indicates the need for backwashing a pressure filter?

The need for backwashing a pressure filter is commonly indicated when the filter becomes clogged. Clogging occurs as particles, sediments, and impurities accumulate on the filter media, leading to a decrease in flow rate and efficiency. When the filter is clogged, the pressure differential across the filter rises because the system is working harder to push water through the blocked spaces. Backwashing helps to restore the filter's functionality by reversing the flow of water, which flushes out the accumulated debris and cleans the filter media. This process is essential for maintaining optimal water filtration and ensuring the longevity and effectiveness of the pressure filter system.

In contrast, a filter that operates smoothly would not require backwashing, as it suggests that the flow rate is adequate and the media is clear. An increase in water supply pressure could indicate a variety of issues, but it does not specifically signal the need for backwashing. Similarly, the addition of chemicals to the system is part of the maintenance procedure and does not inherently indicate that backwashing is needed; it requires careful management to prevent any unwanted buildup. Thus, the correct answer highlights the importance of recognizing when a filter is no longer performing optimally due to clogging.