If no fuel appears at the spray tip while testing a closed fuel injection nozzle, what can be inferred?

In a situation where no fuel is observed at the spray tip during the testing of a closed fuel injection nozzle, it indicates that the needle valve is indeed functioning correctly. The needle valve is responsible for allowing fuel to flow into the nozzle when it is opened by the fuel pressure. If no fuel is coming out, it suggests that the valve is not being actuated, which is consistent with proper operation if it is designed to remain closed in a non-pressurized state.

When you observe this lack of fuel at the spray tip, it typically suggests an issue that is not related to the needle valve operating correctly. The needle valve's proper function means it remains closed when it should be, preventing fuel from escaping when there's no sufficient pressure to open it. This is a key aspect of fuel injector operation, as it helps maintain fuel system pressure and prevents dribbling or leaking of fuel when the engine is not actively injecting.

Understanding this helps clarify the functioning of the fuel injection system and underscores the importance of the needle valve’s role in managing fuel flow under various engine conditions.