🔍 Key Concepts

• Stuffing box purpose in a centrifugal pump (preventing air leakage into the pump along the shaft) • Difference between suction head (positive pressure at suction) and suction lift (pump is above liquid, suction under vacuum) • Effect of low suction pressure / vacuum on pump operation and the need for a sealing (flush) line

💭 Think About

• Ask yourself: When is there a risk of air leaking in around the shaft instead of liquid leaking out? In that case, why would you need a liquid sealing line and seal cages? • Compare a pump that has plenty of pressure at its suction (submerged or flooded suction) with a pump that must lift liquid up from below (vacuum on suction). In which case is a stuffing box sealing liquid most critical? • Look at each choice and decide: which condition most clearly points to a vacuum or very low pressure on the suction side, rather than just low temperature or low discharge pressure?

✅ Before You Answer

• Identify which choice refers specifically to suction under vacuum (suction lift) rather than temperature or discharge pressure. • Verify that a liquid sealing line is mainly needed to prevent air infiltration at the stuffing box when suction pressure is low or negative. • Confirm that options about temperature (150°F) or low discharge pressure (25 psi) do not directly relate to the need for a stuffing box sealing line.