🔍 Key Concepts

• Viscosity control in heavy fuel oil systems and why viscosity must be kept nearly constant at the engine inlet • How a viscosimeter signal is typically used to adjust another component (think: what changes fuel viscosity?) • Reading the flow path on Illustration MO-0077: position of the viscosimeter relative to the final heaters, filters, and injection pumps

💭 Think About

• Starting at the main engine, trace the fuel line backward on the diagram until you reach the viscosimeter. Then see what component upstream would logically be adjusted to correct viscosity. • Ask yourself: does the viscosimeter more likely control a component that changes temperature, a component that changes flow rate/pressure, or a component that changes tank level? Match each answer choice to one of those functions. • For each option, imagine what its "output" is (e.g., temperature, cleaned fuel, pressure, or tank outflow). Which one, if changed, would directly change the viscosity measured at the viscosimeter?

✅ Before You Answer

• Confirm on the diagram what variable each listed component primarily affects: temperature, cleanliness, pressure/flow, or storage level. • Check which component is connected (often by a control line or symbol) to the viscosimeter location; that’s the one whose output is adjusted to keep viscosity constant. • Eliminate any components whose normal job is not to change fuel temperature, since temperature control is the main way to control viscosity in an HFO system.