What device introduces foam concentrate into the water stream in most foam-water systems?

• A. A foam drier.
• B. A foam dump valve.
• C. A foam concentrate metering pump.
• D. A foam concentrate proportioner (inline eductor or external proportioning device).

Answer: (D)

The essential idea is that foam concentrate is mixed into the water stream using a foam concentrate proportioner. In most foam‑water sprinkler systems, the concentrate is stored separately and the proportioner uses the flow of water to draw the concentrate into the water line at the correct ratio. This is typically done with an inline eductor (a venturi device inside the piping) or an external proportioning device connected to the system.

How it works: water flows through the proportioner, creating a suction that pulls foam concentrate from its storage container. The concentrate and water mix to form the foam solution, which then continues to the sprinklers. The ratio is set by the design of the proportioner to achieve the required foam solution strength (for example, a 3% or 6% mix, depending on the concentrate and system requirements).

Other devices have different roles. A foam dump valve is used to remove concentrate from the system under certain conditions, not to introduce it into the water stream. A foam concentrate metering pump can move concentrate but does not inherently introduce it into the water stream; it is typically part of the supply path feeding a proportioner. A foam drier is not the device that adds concentrate into the stream.

Therefore, the device that introduces foam concentrate into the water stream in most foam‑water systems is the foam concentrate proportioner (inline eductor or external proportioning device).