Which of the following is NOT a low-energy foam proportioning system installed on ARFF apparatus?

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

Answer: (C)

Understanding how foam gets mixed with water helps explain why some systems are considered low-energy and others are not. Low-energy foam proportioning relies on the energy already present in the water flow or simple pressure differences to pull foam concentrate into the water stream, without needing a separate pump dedicated to the foam concentrate.

Venturi and eductor devices work on this principle. As water speeds through a constricted passage (Venturi) or through an eductor, foam concentrate is drawn into the flow from a reservoir and mixed automatically. No extra power source is required beyond the water flow, so these are classic low-energy systems.

Balanced-pressure proportioning also falls into the low-energy category because it maintains a fixed foam-water ratio by balancing pressures between the water supply and the concentrate supply, typically without a separate high-pressure concentrate pump.

Direct-injection does not rely on the water’s energy to mix the foam. Instead, it uses a dedicated pump to inject foam concentrate directly into the water line at a controlled ratio, which requires additional energy and equipment. Because of that separate energy requirement, it is not a low-energy system.

So, the system that is not a low-energy foam proportioning method is the one that uses a dedicated foam concentrate pump to inject concentrate directly into the water stream.