Centrifugal fire pumps may operate with which type of intake pressure?

• A. Negative intake pressures
• B. Positive intake pressures
• C. Atmospheric intake pressures
• D. Vacuum intake pressures

Answer: (B)

A centrifugal fire pump relies on having water pushed into the pump, not pulled by it. Positive intake pressure on the suction side provides a pressure push into the impeller, helping the pump develop flow and stay primed. This positive pressure also reduces the risk of cavitation (water vaporizing in the pump) and keeps the suction from collapsing under high flow demand or elevation changes. If the intake were negative or a vacuum, the pump would have to create suction to draw water in, which can drop the inlet pressure below the water’s vapor pressure and cause cavitation or loss of prime. Atmospheric intake pressure offers less margin and can be unreliable under firefighting conditions, so maintaining positive intake pressure is the standard practice.