🔍 Key Concepts

• Closed fuel injection nozzle operation and purpose of the needle valve • Meaning of design valve opening pressure and how a properly set spring affects opening • How orifice condition (eroded vs too small) would change fuel flow at or above opening pressure

💭 Think About

• Ask yourself: If the fuel pressure is slightly BELOW the specified opening pressure, should a correctly working needle valve allow any fuel past the seat? • Which of these options would cause the needle to lift and leak EARLY (before design opening pressure), and which would keep it tightly seated until the correct pressure? • Think about how erosion or very small orifices would affect flow AFTER the needle has already opened, not before.

✅ Before You Answer

• Verify what behavior is expected from a properly adjusted needle valve and spring when pressure is BELOW opening value. • Consider which defect would cause premature opening or leakage rather than no flow at all. • Confirm that orifice erosion mainly affects spray pattern and opening pressure AFTER the valve begins to lift, not when it is still fully seated.