Which of the following are two types of low energy foam proportioning systems installed on Earth apparatus?

The identification of balanced pressure and direct injection as the correct examples of low energy foam proportioning systems reflects an understanding of how foam systems integrate into firefighting equipment.

Balanced pressure proportioning utilizes a system where the foam concentrate is mixed with water at a consistent ratio regardless of changes in flow rate or pressure. This system provides precise control over foam concentration and is effective across varying operational conditions, ensuring that the correct amount of foam concentrate is delivered to the firefighting medium.

Direct injection, on the other hand, injects foam concentrate directly into the water stream using a metering valve. This system allows for quick adjustments of foam concentration and is simpler in design and operation. It is commonly used in many firefighting applications, especially in emergencies where rapid response is necessary.

Both systems serve to enhance the effectiveness of fire suppression by providing reliable foam application, which is critical in combating flammable liquid fires, making them appropriate choices for low energy foam proportioning systems on firefighting apparatus. Other types of systems mentioned in the other options do not fit the criteria for low energy foam proportioning, focusing instead on different methods or operational capacities.