🔍 Key Concepts

• Study how the discharge (delivery) valve isolates the high‑pressure line from the pump barrel after injection. • Understand the idea of effective stroke: only the part of plunger travel that occurs after line pressure reaches nozzle opening pressure actually delivers fuel. • Consider what happens to line pressure and start/stop of injection if fuel can leak back past the discharge valve between pump strokes.

💭 Think About

• When the plunger starts its upward stroke, what must it do to begin injection, and how would a leak at the discharge valve change that requirement? • If pressure in the discharge line bleeds off between injections, does the plunger have to travel more or less before reaching nozzle opening pressure? How does that affect the effective stroke? • Does a leaking discharge valve mainly change the timing of the plunger motion, or the portion of its travel that is actually effective for injection?

✅ Before You Answer

• Be clear on the difference between plunger stroke (mechanical travel) and effective stroke (fuel delivery portion). • Decide whether a leak causes pressure to be retained or lost in the discharge line between strokes, and what that does to the next stroke. • Verify which option (increased or decreased effective stroke) matches the situation where some of the plunger’s movement is spent just rebuilding lost pressure before injection can resume.