🔍 Key Concepts

• Fuel injection nozzle operation – how pressure moves the nozzle valve (needle) off its seat and how it reseats • Relationship between supply port covered/uncovered and pressure acting on the needle valve • Role of a spring at the lower end of the nozzle: which direction it forces the needle and what that does to fuel flow

💭 Think About

• Trace the fuel path: when fuel pressure builds and the supply port condition changes, does the needle tend to move toward opening or closing? How would the spring piece #34 assist or oppose that motion? • Look at the orientation of the needle valve and the direction of spring force at #34. If pressure drops or a port is uncovered, which way will the spring push the needle and what effect does that have on the nozzle valve? • Compare the conditions ‘release port uncovered’ and ‘supply port covered.’ In which condition would you expect fuel injection to stop, and what must the spring piece do to make that happen?

✅ Before You Answer

• Identify clearly which part in the cross‑section is the nozzle valve/needle and which end is the seat where flow stops. • Confirm the direction of spring force from piece #34: is it trying to push the needle onto the seat (closing) or off the seat (opening)? • Decide under which port condition you would normally want the injection to end, and match that with the option that describes the spring’s closing action at that moment.