🔍 Key Concepts

• Positive suction head vs suction lift in centrifugal pumps • How pressure behaves at the stuffing box when liquid level is above the pump centerline • Relationship between internal pump pressure and leakage direction at the shaft stuffing box

💭 Think About

• First, picture the pump with the liquid source level above the pump. Is the suction side under vacuum or positive pressure in this case? • If the suction side is at a higher (positive) pressure than the atmosphere, will fluid tend to move into the pump from outside, or out of the pump along the shaft? • Consider what the stuffing box is trying to prevent: is it mainly trying to stop air getting in or liquid getting out when you have positive suction head?

✅ Before You Answer

• Confirm whether positive suction head means the pump suction pressure is above atmospheric or below atmospheric. • Think about which side has the higher pressure: inside the pump or outside at the shaft: fluid always flows from high to low pressure. • Eliminate any option that suggests a perfectly sealed, no-leakage condition – in real pumps, some controlled leakage at the stuffing box is normal.