Water Mist Sprinkler

The difference is fundamental — they are designed for completely different protection objectives and should never be substituted for each other.

A standard sprinkler head (ZSTX, ZSTZ) is a closed-head device with a thermal sensing element. It activates individually when the temperature at its specific location exceeds the activation threshold, throwing large droplets over a wide floor area below to control a spreading fire. The goal is area fire control — limiting the fire to the sprinkled area.

A water mist / water spray nozzle (ZSTW) is an open-head device with no thermal sensing element. It is part of a deluge system where all nozzles in the zone activate simultaneously when an external detector triggers the deluge valve. The goal is targeted equipment protection — enveloping a specific piece of equipment (transformer, turbine, generator) with fine water mist to cool its surface and suppress ignition. The nozzle positions, spray angles, and flow rates are all engineered to the specific equipment geometry, not to a generic floor area.

Oil-filled power transformers present a very specific fire scenario: burning transformer oil (insulating mineral oil, flash point ~140°C) can spray at high velocity from a ruptured conservator or bushing, creating a pressurised burning oil jet that is extremely difficult to suppress with large water droplets. The fine, high-velocity mist from a centrifugal nozzle achieves three things simultaneously that the impact type cannot match: (1) it penetrates the burning oil jet and reaches the ignition source; (2) fine droplets evaporate almost instantly on contact with hot oil, absorbing heat rapidly; and (3) the high droplet density creates an oxygen-excluding atmosphere around the transformer body that suppresses secondary ignition of oil films on the tank surface.

The impact (medium-velocity) ZSTW C type is effective for surface cooling and general area wetting — where the fire is a pool or surface fire, not a pressurised jet. For cable trays, open vessel surfaces, and rain-down cooling, the ZSTW C is appropriate and more economical. For transformer and turbine protection, specify ZSTW B.

Yes — this is critical for centrifugal (high-velocity) nozzles. The ZSTW B series has a very small internal orifice (particularly in the K12 to K27 range) that is vulnerable to blockage by pipe scale, weld debris, sand, or any particulate matter that may be present in the water supply or the pipe system. Blockage of even a single nozzle creates a gap in the protection coverage around the equipment — a potentially catastrophic failure mode in a system designed to protect a high-value transformer or turbine.

CA-FIRE offers the ZSTW B with integral filter screen (带过滤网) which incorporates a 40-mesh stainless steel screen at the nozzle inlet. This is the recommended option for all new transformer and turbine spray systems. Where the standard (non-filtered) ZSTW B is installed, a Y-type strainer must be fitted at the start of each branch line supplying the nozzles, and the strainer must be included in the routine maintenance schedule with annual cleaning or inspection.

For transformer and turbine protection (the primary application of ZSTW nozzles), UV/IR flame detectors are the standard activation method. These optical detectors respond to the UV and infrared radiation emitted by a flame within milliseconds of ignition — far faster than any heat-based detection method. Given that a transformer oil fire can transition to a full-scale blaze within seconds, UV/IR detection is considered mandatory for oil-filled equipment protection in most jurisdictions.

Heat detectors or linear heat detection cable may be used as a secondary or cross-zoned detection method to prevent false activations from welding, arc flash, or other transient UV sources. The standard approach is a cross-zoned UV/UV or UV/IR configuration where two independent detector channels must both trigger before the deluge valve opens, reducing nuisance activation risk.

Manual activation (emergency pushbutton) must always be provided as a backup, allowing operators to activate the system without waiting for automatic detection in an emergency. Confirm the specific detection and activation requirements with the relevant standard (GB 50229 for power installations; NFPA 15 / NFPA 850 for general water spray and power plant applications).

No — the CA-FIRE ZSTW B and C series are designed for medium-pressure fixed water spray systems operating at a rated pressure of 0.35 MPa (approximately 3.5 bar). They are not high-pressure water mist (HPWM) nozzles. High-pressure water mist systems operate at 35–100 bar and use specialist stainless steel nozzles with sub-millimetre orifices, engineered to produce ultra-fine droplets (DV50 below 200 µm) that suppress fires by oxygen displacement and cooling in enclosed spaces.

HPWM systems are appropriate for engine rooms, turbine enclosures where total flooding suppression is required, heritage buildings, and data centres where water damage from conventional sprinklers is unacceptable. If a high-pressure water mist system is required for your application, contact CA-FIRE to discuss the appropriate system specification — these are engineered-to-order systems requiring detailed hazard assessment, not standard catalogue items.

For the protection applications described on this page (transformers, turbines, cable tunnels, outdoor vessel cooling), the ZSTW B and C medium-pressure series are the correct and code-compliant specification.