The LWF Blog

Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 274

February 16, 2026 10:37 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 273, LWF discussed proportioners, and in particular, inductors and bladder tanks. In part 274, we continue exploring the different elements of foam proportioning by talking about balanced pressure proportioning and water-driven foam metering pumps.

 

Balanced Pressure Proportioning Systems

A balanced pressure proportioning system is a fire suppression system designed to precisely introduce foam concentrate into a water stream and is adaptable to varying flow rates and pressures. Equal pressure is maintained in both the foam and water lines to guarantee an accurate and consistent mixing ratio.

The system comprises a foam concentrate pump which draws from an atmospheric storage tank. Foam concentrate is pumped through a pressure balancing valve into a proportioner. The pressure balancing valve senses both foam and water pressures and regulates the foam pressure down to match the water pressure, ensuring an accurate ratio.

In a similar way to a bladder tank system, it is able to operate over a wide range of flows and pressures, depending upon the proportioner and the foam concentrate. A balanced pressure proportioning system is commonly-used in high-hazard industrial, marine and aviation environments for fire protection.

 

Water-driven Foam Metering Pumps

A water-driven foam metering pump uses a water-powered motor installed in the foam system’s water line to operate a foam pump that draws concentrate from an atmospheric storage tank. The output of the foam pump is synchronized with the speed—and therefore the flow rate—of the water motor, ensuring the correct proportion of foam concentrate is added to the water downstream of the motor.

Water-driven foam metering pumps provide accurate proportioning across a limited range of flow rates and pressures and are available in a wide variety of sizes and capacities, including systems capable of handling many thousands of litres per minute. Recently, they have grown in popularity due to their suitability for both fixed and mobile foam systems. The proportioners are typically skid-mounted or supplied in a form that allows easy installation on vehicles.

In part 275 of LWF’s series on fire engineering we will talk about premix foam units, before beginning to look at the types of foam system available. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.