When reviewing log books, the main salt water cooling pump discharge pressure has decreased in the three years since overhaul. Which of the following would most likely be the cause of the problem.

Correct Answer: Option C — Increased impeller and wear ring clearance.

Increased clearance between the impeller and wear rings allows internal recirculation of fluid within the pump casing. This 'slippage' reduces the effective discharge pressure and flow rate over time. This is a classic symptom of long-term wear in centrifugal pumps, necessitating an overhaul to restore design performance.