How closed-loop marine steam systems work

How does a closed-loop steam system circulate water, and why does it still suffer losses?

A condenser turns exhaust steam back into water for pumping to the boiler, but leakage and system-specific exhaust paths prevent perfect recovery.

No steam system is perfectly sealed, and the panel even notes that copper pipework allows small losses. The boiler is the hottest and highest-pressure part of the circuit, so steam moves through the machinery toward the cooler end. Condensing saturated steam back into water shrinks its volume and creates the low-pressure or vacuum condition that keeps the flow moving in one direction. Feed pumps then return the hot condensate to tanks or the boiler circuit. Leakage and any open exhaust path explain why a nominally closed loop still needs replacement water.