Which method of foam proportioning is described as using a variable output foam pump?

The method of foam proportioning that utilizes a variable output foam pump is the balanced pressure proportioner. This system is designed to maintain a consistent foam-to-water ratio regardless of changes in water pressure or flow. The balanced pressure proportioning system effectively adjusts the foam and water flow rates during operation, allowing for optimal mixing and application of foam, which is critical in fire suppression.

Unlike other methods of foam proportioning, such as self-educting nozzles or in-line eductors that rely on different mechanisms for mixing foam concentrate with water, balanced pressure proportioners can adapt to varying conditions to ensure effectiveness. This makes them particularly beneficial in dynamic firefighting scenarios where maintaining the correct proportion is vital for controlling and extinguishing fires.

Other options do not feature a variable output foam pump but rather operate based on fixed ratios or rely on suction and pressure differentials to mix the foam and water.