A typical yacht system flows from deck filler to tank, pickup, shut-off valve, primary filter and water separator, lift pump, engine-mounted secondary filter, high-pressure injection equipment and injectors. Unused fuel commonly returns to the tank.
The low-pressure side
Tiny air leaks may admit air without leaking visible fuel, especially on suction lines. Suspect loose fittings, damaged hose, filter seals, drain plugs, corroded pickup tubes and poorly seated elements. A restriction can come from tank debris, a blocked vent, collapsed hose, shut valve or clogged filter.
A vacuum gauge fitted at the primary filter can reveal a growing restriction before the engine loses power. Duplex filters allow one element to be brought online while the other is serviced, but only if the valve positions are understood and the installation is appropriate.
The high-pressure side
Injection pumps and injectors meter and atomise fuel at exact timing. Common-rail systems operate at pressures capable of injecting fuel through skin. Do not loosen common-rail pipes or place hands near a suspected leak. Depressurisation and testing require the manufacturer’s procedure and specialist equipment.
Tank design and management
A good installation provides accessible shut-offs, a serviceable primary filter, inspection or cleaning access where practicable, a correctly routed vent and a way to remove water from the lowest point. Fuel polishing can circulate fuel through filtration, but it does not repair a corroded tank or replace physical removal of settled sludge.
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