Which of the following proportioning methods depends on the Venturi principle to draw foam?

Eduction is the correct choice because it utilizes the Venturi principle, which is a fluid dynamics effect where a fluid’s velocity increases as it passes through a constricted section of pipe, resulting in a drop in pressure. In an eductor system, when water flows through a nozzle, it creates a vacuum that draws foam concentrate into the water stream. This mixture is then propelled through the hose to create a foam that can effectively suppress fires.

This method is commonly used in firefighting because it allows for precise control over the foam solution being applied and is effective for producing a consistent foam blanket over a fire. The efficiency of this method makes it suitable for various applications in fire suppression.

The other methods mentioned, like batch mixing, bladder tanks, and direct injection, do not rely on the Venturi principle for drawing foam. Batch mixing involves pre-mixing the foam concentrate with water in a tank before application; bladder tanks store foam concentrate in a pressurized tank; and direct injection injects the foam concentrate directly into the water line without creating a vacuum effect.