Under what pumping condition should you switch from pressure to volume mode?

• A. When the engine RPM is too high
• B. When more than half the rated capacity of the pump will be needed
• C. When the intake valve leaks
• D. When the discharge temperature rises

Answer: (B)

In this scenario, the pump has two ways to be controlled: pressure mode, which tries to hold a set discharge pressure, and volume mode, which focuses on delivering a certain flow (GPM) while allowing pressure to adjust. When you anticipate needing more than about half of the pump’s rated capacity, sticking with pressure mode would force the pump to push a high head to maintain that pressure, which can push the engine and pump beyond efficient operating range. Switching to volume mode shifts the goal to delivering the needed water volume, keeping the engine in its efficient range and avoiding overburdening the pump with maintaining high pressure. The other conditions listed don’t accurately indicate switching modes; they relate to different symptoms rather than the flow-demand mode change.