Which configuration describes an inline balance-pressure proportioning system?

Which configuration describes an inline balance-pressure proportioning system?

• A. A balance-pressure proportioning system utilizing a foam concentrate pump discharging through a metering orifice into a proportioning controller with the foam concentrate and water pressure automatically maintained as equal by a pressure balancing valve.
• B. A balance-pressure proportioning system utilizing a pressure proportioning tank with a diaphragm or bladder to separate the water and foam concentrate discharging through a metering orifice into a proportioning controller.
• C. An inline balance-pressure proportioning system utilizing a foam concentrate pump or bladder tank. A pressure regulating device placed in the pump return line shall maintain constant pressure in the foam concentrate supply line at all design flow rates. This constant pressure shall be greater than the maximum water pressure under all operating conditions.
• D. Foam concentrate pump discharging through a metering orifice into the protection system riser with the foam pressure at the upstream side of the orifice exceeding the water pressure in the system riser by a specific design value.

Answer: (C)

Inline balance-pressure proportioning relies on keeping the foam concentrate at a constant pressure that is higher than the water pressure, so the concentrate is drawn into the water flow through the metering orifice at a stable rate. This is achieved by a pressure-regulating device in the foam concentrate supply line (often in the pump return line) that maintains a constant concentrate pressure across all design flow rates. The key is the constant concentrate pressure and the deliberate pressure difference above the water line, which together ensure a steady and predictable foam-to-water ratio as system pressures vary during operation. This description matches the inline arrangement because it explicitly uses a foam concentrate pump or bladder tank with a regulator in the concentrate line to hold the constant pressure above the maximum water pressure, ensuring reliable proportioning through the metering orifice. The other configurations described either rely on equalized pressures without a controlled higher concentrate pressure, use a bladder/tank arrangement that isn’t inline balance-pressure, or imply a differential without the required constant regulating element, which are distinct approaches from inline balance-pressure systems.

Inline balance-pressure proportioning relies on keeping the foam concentrate at a constant pressure that is higher than the water pressure, so the concentrate is drawn into the water flow through the metering orifice at a stable rate. This is achieved by a pressure-regulating device in the foam concentrate supply line (often in the pump return line) that maintains a constant concentrate pressure across all design flow rates. The key is the constant concentrate pressure and the deliberate pressure difference above the water line, which together ensure a steady and predictable foam-to-water ratio as system pressures vary during operation.

This description matches the inline arrangement because it explicitly uses a foam concentrate pump or bladder tank with a regulator in the concentrate line to hold the constant pressure above the maximum water pressure, ensuring reliable proportioning through the metering orifice. The other configurations described either rely on equalized pressures without a controlled higher concentrate pressure, use a bladder/tank arrangement that isn’t inline balance-pressure, or imply a differential without the required constant regulating element, which are distinct approaches from inline balance-pressure systems.