Why is it important to keep the suction line free of air during pump operations?

• A. Air in suction reduces prime and can cause cavitation and loss of discharge pressure.
• B. It increases discharge line friction.
• C. It improves engine RPM.
• D. It has no effect on prime.

Answer: (B)

Keeping the suction line free of air is essential because air on the suction side interrupts the water column the pump must pull, preventing proper priming. When the suction is flooded with water and free of air, the pump can develop and maintain prime, delivering a stable flow to the discharge.

If air enters the suction, the pump can lose prime, flow becomes inconsistent, and the local pressure in the impeller region can drop below the water’s vapor pressure. That causes cavitation, which damages components, reduces discharge pressure, and lowers overall pump performance.

So the main reason is to maintain prime and prevent cavitation, ensuring the pump can deliver the rated discharge. The idea that air on the suction line simply increases discharge line friction isn’t the correct mechanism, and the other options don’t address the real impact on priming and pressure.