Which of the following is NOT a low energy foam proportioning system?

Low energy foam proportioning systems are designed to mix foam concentrate with water in a way that minimizes energy input during the process, ensuring that the foam is effective yet gentle on the various types of fuels involved in an incident.

Direct injection is not categorized as a low energy foam proportioning system because it involves a high-energy method of introducing foam concentrate directly into the water stream. This process utilizes a pump to inject the foam, which can cause turbulence and a high shear rate. This contrasts sharply with systems like batch mixing, installed in-line eductors, and balanced pressure systems, which utilize water flow and pressure differentials to draw and mix foam gently, maintaining the integrity of the foam solution.

Batch mixing involves preparing a foam solution in a large tank, which does not require continuous mixing under high energy, while in-line eductors rely on the principle of venturi effect to mix foam, also minimizing energy. The balanced pressure system uses proportional blending of water and foam but is carefully controlled to prevent excess energy input, making it suitable for sensitive applications. Therefore, direct injection stands apart as the option that does not conform to the principle of low energy foam proportioning.