Which of the following options correctly lists one of the two low-energy foam proportioning systems installed on ARFF apparatus?

• A. Direct-injection and balanced pressure
• B. Direct-injection and Venturi
• C. Balanced pressure and Venturi
• D. Direct-injection and Eductor

Answer: (A)

On ARFF apparatus, foam proportioning systems are differentiated by how much energy they require to mix foam concentrate with water. The two low-energy options are direct injection and balanced pressure.

Direct injection places a foam concentrate metering device directly into the water line so the concentrate is injected into the water flow as it passes through, controlled by a ratio controller. This method is simple, compact, and maintains a stable foam-to-water ratio across a wide range of pump pressures and flow rates with minimal energy loss.

Balanced pressure uses a separate foam concentrate supply that is pressurized, with a metering valve that introduces concentrate into the water line while maintaining equal pressure on the foam and water sides. This balance preserves accurate proportioning even as water flow changes, offering reliable performance without relying on high-velocity water flow to draw the concentrate.

Venturi and eductor systems rely on the energy of the moving water to entrain foam concentrate, which makes them higher-energy proportioners and more sensitive to flow and pressure variations. That’s why they’re not classified with the low-energy options.

So, direct injection and balanced pressure are the two low-energy foam proportioning systems installed on ARFF apparatus.