What is the purpose of a low-suction-pressure switch?

• A. To shut the pump off if suction pressure drops
• B. To detect suction pressure loss and cause automatic pump start to prevent cavitation
• C. To monitor discharge pressure downstream
• D. To auto-adjust motor speed

Answer: (B)

The purpose of a low-suction-pressure switch is to sense a drop in suction pressure on the pump intake and automatically start the fire pump when that pressure falls below a set point. This immediate start helps keep suction pressure from collapsing further, reducing the risk of cavitation—where vapor bubbles form and damage the impeller and reduce pumping capability—and ensures the system can deliver water when demand rises. It’s about automatic protection and readiness on the suction side, not about shutting the pump off, monitoring discharge pressure, or changing motor speed.