Which arrangement is used to protect potable water lines used for priming non-potable water pumps on sewage pumps?

• A. Check valve
• B. Isolation valve only
• C. Secondary feed tank with an air gap
• D. Backflow preventer with relief valve

Answer: (C)

The important idea here is preventing backflow from the sewage pump priming system into the potable water supply. Using a secondary feed tank with an air gap creates a physical separation between the potable supply and the non-potable priming water. The potable water fills the tank, while the non-potable pump draws from the tank side that is isolated by the air gap. That air gap acts as a fail-safe barrier: even if pressure in the non-potable line tries to push water back, there’s no direct connection to the potable supply, so contamination cannot be drawn back into the clean system. This arrangement provides robust protection against back-siphonage and backflow.

Other options don’t offer the same level of protection in this priming setup. A simple check valve can stop reverse flow but may fail or be bypassed during suction events; an isolation valve alone doesn’t protect against backflow; and a backflow preventer with relief valve adds complexity and may not guarantee the same simple, reliable separation as a dedicated air gap with a secondary tank for priming needs.