Which statement best describes a duplex sea strainer?

• A. Two elements with a valve to direct flow to one element or the other
• B. A single element with a bypass option
• C. Two levels of filtration without valves
• D. A coarse mesh filter only

Answer: (A)

The key idea is redundancy with a way to switch flow between two filters. A duplex sea strainer uses two filtration elements and a valve that directs the seawater to one element or the other. This lets one element be isolated and cleaned while the other continues to draw seawater, keeping the system flowing with minimal downtime.

Why this best describes it: having two elements plus a valve to switch which one is in use provides uninterrupted filtration and allows maintenance without shutting the whole intake down. The other descriptions don’t fit because a single element with bypass misses the second element and the switching capability; two filtration levels without valves lack a means to isolate or switch between them; and a coarse mesh filter alone doesn’t capture the duplex, valve-enabled setup.