The LWF Blog
Fire Safety Engineering for Design – Water Mist Components – Part 306
September 28, 2026 8:56 amLWF’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 305, LWF began to look at water mist components, starting with pumps. In part 306, we will continue discussing water mist components by looking at nozzles and valves.
Water mist fire protection systems depend on carefully matched components to deliver water at the correct pressure and in the required form. Nozzles determine how the water is discharged, while valves control when and where it enters the protected area. Selecting these components requires consideration of operating pressure, system configuration and the method used to activate the system.
Nozzles are available in several designs to suit different operating pressures and applications. High-pressure systems operating at 50 bar and above use nozzles with small orifice outlets. These are available as automatic or deluge types, depending on the way the system is designed to respond to fire.
Lower-pressure systems operating at 12 bar and below use a different nozzle arrangement. The design is similar to a conventional sprinkler but incorporates a smaller orifice and specially designed deflector plates. Automatic and deluge versions are available. A third option is the twin-fluid nozzle, which combines propellant gas and water at the outlet orifice. Twin-fluid nozzles are available for deluge applications only.
Nozzle selection therefore needs to reflect the pressure and operating principle of the complete system. Requirements for the construction and performance of open and automatic water mist nozzles are covered by BS 8663-1:2019.
Valves provide the control needed to isolate, activate and manage different sections of a water mist installation. Isolation valves are installed upstream of zone or alarm valves and deluge valves, allowing parts of the system to be isolated during maintenance. Valve position should be monitored so that an open or closed condition can be identified. For higher-pressure applications above 70 bar, ball valves are commonly used, while butterfly, gate or ball valves may be used at pressures of 16 bar and below.
Zone or alarm valves are used in wet automatic systems to divide a protected building into separate sections. A typical assembly incorporates a non-return valve, flow switch, drain and test valve, and pressure gauges. These components provide control and allow important operating conditions to be monitored.
Deluge valves serve a different purpose. They are used in deluge systems and can be activated electrically through a solenoid or pneumatically using a separate air supply. Ball-valve arrangements are used at pressures of 50 bar and above, while diaphragm or ball valves can be used below 16 bar. Some designs provide remote resetting. Valves can also be configured to remain latched open until they are manually closed.
Pre-action valves are suited to applications where unwanted water discharge needs to be minimised. The upstream side of the system contains water, while the downstream pipework remains dry and is filled with air. Air pressure is monitored so that a loss of pressure can indicate a problem with system integrity. Following detection of a fire, the detection system signals the valve to open and water enters the pipework. Discharge from the automatic system occurs when sufficient heat operates the thermal bulb or bulbs.
The electrical interface between detection systems and water mist or sprinkler systems is addressed by BS 7273-3:2008 for pre-action water mist and sprinkler systems.
For water mist systems other than pre-action systems, BS 7273-5:2008 covers electrical actuation arrangements and the interface with fire detection and fire alarm systems.
The effectiveness of a water mist installation depends on these components working together as an engineered system. Nozzles, valves, detection and actuation arrangements must be compatible with the operating pressure and the specific protection strategy. Careful selection and configuration are therefore fundamental to achieving the intended fire protection performance.
In part 307 of LWF’s series on fire engineering we will continue our discussion of water mist system components by discussing pipes and pipework. 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.