🔍 Key Concepts

• How a positive displacement pump behaves when discharge resistance changes • Difference between pressure control and flow control devices • What happens to pump output when engine (driver) speed changes

💭 Think About

• Ask yourself: In a positive displacement rotary gear pump, what determines how much fluid is moved per revolution, and what determines how many revolutions occur per minute? • Which listed device mainly protects the system from overpressure, and which one actually varies the amount of fluid delivered into the system under normal operation? • If the discharge line becomes partially blocked, which of these options would keep the flow rate through the system at the desired value rather than just limiting maximum pressure?

✅ Before You Answer

• Clarify the role of a pressure relief valve (safety/overpressure protection vs. normal flow control) • Clarify the role of a pressure regulating valve (maintaining set pressure which secondarily affects flow) • Remember that a positive displacement pump moves a fixed volume per revolution, so verify what factor changes the volume per unit time (flow rate).