What does the transfer valve do in a two-stage centrifugal pump?

• A. Directs water flow and switches between Volume mode (parallel) and Pressure mode (series)
• B. Increases engine RPM
• C. Reduces friction loss in hoses
• D. Controls nozzle pattern

Answer: (A)

In a two-stage centrifugal pump, the transfer valve controls how the two pump stages are connected, allowing you to switch between operating modes that trade flow for pressure. When set for volume mode, the stages run in parallel, so both impellers contribute to the discharge at once, giving higher flow with lower overall pressure. When set for pressure mode, the water from the first stage flows into the second stage, adding the pressures of both stages to produce higher discharge pressure with reduced flow. This switching capability lets you tailor the pump output to the firefighting need—more gallons per minute for long lays or larger lines, or more pressure for shorter distances or smaller nozzles. The transfer valve doesn’t change engine RPM, isn’t about reducing friction losses in hoses, and doesn’t control the nozzle pattern; those aspects are handled by engine speed, hose/line characteristics, and nozzle design.