Which condition must be maintained to ensure continuous water supply when drafting?

• A. Neutral suction pressure
• B. Positive suction pressure to maintain prime and prevent cavitation.
• C. Negative suction pressure
• D. Zero suction pressure

Answer: (B)

Maintaining positive suction pressure on the pump’s suction side is essential to keep the pump primed and to prevent cavitation. When drafting, the pump relies on suction to pull water into the impeller. If suction pressure drops to zero or becomes negative, air can enter the suction line or the water column can vaporize, causing cavitation and the loss of prime. With positive suction pressure, the suction line stays filled with water, ensuring a continuous supply to the pump and the ability to develop discharge pressure. In practice, this means keeping the suction line free of leaks and restrictions, ensuring the source remains fully primed (submerged or otherwise pressurized as needed), and not allowing the suction pressure to fall toward zero or negative.