What is controlled by monitoring the water flow and controlling the speed of a positive displacement foam concentrate pump?

• A. Direct injection system
• B. Variable flow
• C. Fixed flow
• D. Manual throttle

Answer: (B)

The key idea is foam proportioning that adjusts automatically based on the water flowing through the system. With a positive displacement foam pump, the amount of concentrate delivered is tied to the pump speed. By monitoring the water flow and feeding that information back to the pump controller, the system can vary the pump speed to keep the foam concentrate-to-water ratio constant as flow changes. When water flow increases, the controller speeds up the pump to deliver more concentrate; when flow drops, it slows the pump to maintain the same mix. This behavior is what defines a variable flow foam proportioning system. A fixed flow would push the same amount of concentrate regardless of water flow, and a manual throttle would require operator action rather than automatic feedback based on water flow. A direct injection system pertains to a different arrangement of concentrate addition and isn’t the automatic flow-adjusting method described here.