A ______ shows when DHC of a filter has been reached.

• A. Bypass indicator
• B. Pressure gauge
• C. Flow meter
• D. Relief valve

Answer: (A)

Differential head across a filter climbs as the filter traps more debris, increasing resistance to flow. When that differential head reaches its preset limit, the system can divert flow around the filter to keep water moving, and a bypass indicator shows that this condition has been reached. This means the filter should be serviced or replaced soon to restore proper filtration.

The other instruments don’t serve this specific signaling role: a pressure gauge measures overall pressure, not the drop across the filter; a flow meter tracks how much water is moving but not how much the filter is restricting it; a relief valve releases excess pressure but doesn’t indicate that the filter’s head loss threshold has been met.