Deluge systems are designed for hazards where rapid application of water over a protected area may be required. This guide explains open sprinklers and nozzles, deluge valves, detection, releasing control panels, solenoids and fire alarm interfaces from a technician's perspective.
What Is a Deluge Fire Sprinkler System?
A deluge fire sprinkler system is a water-based fire protection system that uses open sprinklers or open spray nozzles connected to piping controlled by a deluge valve.
Unlike the automatic sprinklers commonly found on wet and dry pipe systems, the discharge devices on a deluge system are normally open. They do not each contain a heat-responsive element that must operate before water can discharge.
During normal conditions, water is held back from the system piping by the deluge valve.
When the approved releasing arrangement operates, the deluge valve opens and allows water into the system piping. Because the sprinklers or nozzles are open, water can then discharge from the open outlets throughout the hydraulically designed deluge system.
How Does a Deluge Sprinkler System Work?
The exact sequence depends on the listed deluge valve and releasing method, but an electrically released system can be understood like this:
Fire Condition → Detection Operates → Releasing Control Unit Processes Input → Releasing Circuit Operates → Solenoid/Releasing Device Operates → Deluge Valve Opens → Water Enters Piping → Water Discharges From Open Outlets
That sequence is very different from a conventional wet or dry pipe sprinkler system.
On a wet or dry pipe system, individual automatic sprinklers normally remain closed until heat operates their heat-responsive elements.
On a deluge system, the discharge devices are already open. The releasing arrangement controls the valve that admits water to the system.
What Is an Open Sprinkler?
An open sprinkler does not contain the heat-responsive operating element found in a conventional automatic sprinkler.
There is no glass bulb or fusible element holding the sprinkler closed.
That means an open sprinkler does not independently wait for heat at that individual sprinkler before allowing water to discharge.
Once the deluge valve opens and water reaches the system piping, water can discharge through the open sprinklers or nozzles supplied by the system.
What Is a Deluge Valve?
The deluge valve is the water-control valve separating the water supply from the normally dry downstream deluge piping.
During normal conditions, the valve remains set and prevents water from entering the system piping.
When its listed releasing arrangement operates, the valve opens and allows water to enter the system.
The exact internal construction and release method vary by manufacturer and valve model. Technicians should therefore use the manufacturer's installation, operation and maintenance documentation for the specific valve installed.
Does a Solenoid Valve Hold Back All the Sprinkler Water?
This is an important terminology correction.
On an electrically released deluge system, a solenoid valve can be part of the releasing trim, but the solenoid itself should not simply be described as the main valve holding back all of the sprinkler-system water.
In a common electrically released arrangement, the solenoid controls pressure associated with the deluge valve's release or priming chamber.
When the releasing control unit commands the solenoid to operate, the release arrangement allows the deluge valve itself to open.
Releasing Panel → Solenoid/Releasing Device → Deluge Valve → Water Into System
Are All Deluge Systems Electrically Released?
No.
Electrical release is common and especially important to fire alarm technicians, but deluge valves can be associated with different listed releasing methods depending on the system design and equipment.
Releasing arrangements can include:
- Electric releasing systems
- Pneumatic releasing systems
- Hydraulic releasing systems
- Listed heat-responsive releasing devices
- Manual emergency release arrangements
- Combinations permitted by the listed system design
For that reason, it is inaccurate to say that every deluge system requires a smoke detector, electronic solenoid and fire alarm panel to operate.
How Does an Electrically Released Deluge System Work?
An electrically released deluge system is where the fire alarm/releasing interface becomes especially important.
Compatible initiating devices are connected to a control unit listed for the required releasing service.
Depending on the approved system design, detection might involve devices such as:
- Heat detectors
- Smoke detection where appropriate for the application
- Flame detectors
- Other listed detection technologies suitable for the protected hazard
When the required initiating condition is satisfied, the releasing control unit operates the releasing circuit connected to the appropriate releasing device, such as a solenoid valve.
That operation causes the deluge valve to open according to its listed design.
Can Any Fire Alarm Panel Release a Deluge System?
No.
Automatic releasing service is a specialized fire alarm control function.
The control equipment, initiating devices, releasing circuits, releasing devices and overall system arrangement must be compatible and suitable for the required releasing application.
A technician should never assume that an ordinary notification appliance circuit or generic relay output can simply be connected to a deluge solenoid because the voltage happens to match.
What Happens When the Deluge Valve Opens?
Once the deluge valve opens, water enters the downstream piping.
Because the discharge devices are open, water does not have to wait for individual sprinkler heat-responsive elements to operate.
Water can discharge through the open sprinklers or spray nozzles supplied by the activated deluge system.
This rapid, simultaneous application of water across the protected design area is one of the defining characteristics that separates deluge protection from conventional wet and dry pipe sprinkler systems.
Where Are Deluge Systems Used?
Deluge systems are associated with special hazards and exposures where rapid water application can be appropriate.
Applications can include certain:
- Industrial hazards
- Flammable or combustible liquid hazards
- Power-generation facilities
- Aircraft-related facilities
- Process equipment
- Transformers and similar special hazards
- Exposure-protection applications
- Other high-challenge hazards requiring specifically designed water application
The correct protection method depends on the actual hazard and applicable fire-protection standard. A deluge system should not be assumed to be appropriate merely because an occupancy is considered "high hazard."
Does Detection Have to Be Smoke or Heat?
No single detection technology is correct for every electrically released deluge application.
The detection method should be selected for the specific hazard, environmental conditions, required response and approved system design.
For example, some hazards may benefit from heat detection, while others can require a different listed detection technology capable of responding appropriately to the anticipated fire signature.
This is why copying a conventional building smoke-detection layout and using it to release a special-hazard system without engineering the complete sequence can create serious problems.
What Does the Fire Alarm/Releasing System Monitor?
An electrically released deluge installation can contain several monitored conditions.
Depending on the listed equipment and approved design, these can include:
- Automatic initiating devices
- Manual release devices
- Releasing circuit integrity
- Deluge valve supervisory conditions
- Waterflow or alarm pressure
- Control-valve position
- Power-supply conditions
- Other required system supervisory or trouble conditions
The exact points vary with the system, which is why technicians should work from the approved sequence of operations and manufacturer's documentation rather than assuming every deluge installation is wired identically.
Supervising the Electric Releasing Device
The releasing device is one of the most critical pieces of an electrically released deluge system.
Modern listed arrangements can provide supervision intended to detect conditions such as removal or disconnection of an electric actuator so the releasing system is not unknowingly left incapable of operating as intended.
This is a good example of why a deluge system requires more than simply supplying voltage to a solenoid.
The integrity of the complete releasing path matters.
Manual Release of a Deluge System
Deluge systems can also incorporate a manual emergency releasing method as part of the listed system arrangement.
Manual release is different from an ordinary building manual fire alarm box.
A device specifically provided for releasing service is intended to initiate the required extinguishing-system sequence according to the approved design.
Deluge vs Wet Pipe Sprinkler Systems
| Feature | Wet Pipe | Deluge |
|---|---|---|
| Normal piping condition | Filled with water | Downstream piping normally not filled with water |
| Discharge devices | Closed automatic sprinklers | Open sprinklers or nozzles |
| What admits water? | Water is already in the piping | Operation of deluge valve |
| Separate releasing system | Not normally required for sprinkler operation | Required to operate the deluge valve according to system design |
For the conventional water-filled system, see: Wet Pipe Fire Sprinkler Systems | How They Work →
Deluge vs Dry Pipe Sprinkler Systems
Deluge and dry pipe systems can both have downstream piping that is not normally filled with water, but that similarity should not cause them to be confused.
A dry pipe system normally uses closed automatic sprinklers and pressurized air or nitrogen in the sprinkler piping. Operation of an automatic sprinkler causes pneumatic pressure loss that ultimately allows the dry pipe valve to operate.
A deluge system uses open sprinklers or nozzles and a separate releasing arrangement to operate the deluge valve.
See: Dry Pipe Fire Sprinkler Systems | How They Work →
Deluge vs Preaction Sprinkler Systems
Deluge and preaction systems are especially easy to confuse because both can use similar valve equipment and electric releasing components.
The major difference is downstream operation.
A deluge system normally uses open sprinklers or nozzles. Once the deluge valve opens, water can discharge through the open outlets.
A preaction system normally uses closed automatic sprinklers. Releasing-system operation can admit water into the sprinkler piping, but an automatic sprinkler must also be open before water can discharge from that sprinkler.
Deluge: Valve opens + outlets already open = water discharges.
Preaction: Valve opens + sprinklers still closed = piping can fill, but water does not discharge until an automatic sprinkler opens, depending on the specific preaction arrangement.
Does a Deluge System Have a Waterflow Alarm?
The deluge installation must provide the required alarm and supervisory functions for the particular system.
Pressure-operated alarm equipment can be associated with the valve trim so operation of the water-based system produces the required alarm indication.
For fire alarm technicians, it is important to distinguish between:
- Detection/releasing input: The condition that commands system release
- Releasing output: The circuit or device that causes the valve to operate
- Waterflow/alarm confirmation: The condition associated with actual water-system operation
- Supervisory conditions: Abnormal conditions affecting system readiness
- Trouble conditions: Faults involving monitored electrical pathways or equipment
Those functions should not be casually combined into one generic "deluge" point at the fire alarm control unit.
Detection Is Not the Same as Waterflow Confirmation
This distinction is extremely important when troubleshooting an electrically released deluge system.
An initiating detector operating tells the releasing control unit that the required detection condition has occurred.
That does not by itself prove that the deluge valve physically opened or that water entered the system piping.
A technician should understand the complete sequence and determine what feedback or alarm devices are provided to confirm the actual water-system operation.
What Happens if the Releasing Circuit Fails?
A fault in the releasing pathway can prevent an electrically released system from operating as intended.
That is why releasing circuits and associated equipment require the appropriate electrical supervision and why releasing-service equipment cannot be treated like an ordinary convenience-control circuit.
A trouble condition involving the releasing pathway deserves immediate attention because it can represent a problem with the system's ability to release automatically.
Common Deluge System Fire Alarm Mistakes
- Calling deluge simply another type of dry pipe system.
- Assuming every deluge system is electrically released.
- Calling the solenoid the main valve holding back the sprinkler water.
- Assuming every deluge system uses smoke detectors.
- Using an ordinary fire alarm output without verifying releasing-service compatibility.
- Confusing detection with confirmation of actual waterflow.
- Confusing a standard manual fire alarm box with a manual releasing device.
- Assuming deluge sprinklers contain glass bulbs or fusible elements.
- Assuming only one sprinkler or nozzle will discharge after the deluge valve opens.
- Testing releasing equipment without understanding the potential for an actual water discharge.
Testing an Electrically Released Deluge System
Testing a deluge system requires careful coordination because an unintended release can produce significant water discharge and property damage.
Testing procedures should follow the approved system documentation, applicable inspection and testing requirements and the manufacturer's instructions for the installed equipment.
From the fire alarm/releasing side, technicians should understand and verify the applicable portions of the sequence, including:
- Initiating-device operation
- Required releasing logic
- Releasing-circuit supervision
- Manual release where provided
- Required supervisory and trouble signals
- Waterflow or alarm confirmation
- Required annunciation and signal transmission
What About Foam-Water Deluge Systems?
Some special-hazard applications use foam-water systems in conjunction with deluge-type protection.
These systems require specialized design involving the applicable hazard, listed equipment, foam concentrate and proportioning/discharge arrangement.
They should not be described simply as ordinary sprinkler water with "a little foam mixed in."
Fire Alarms Online also does not recommend treating AFFF as the generic answer for every foam application. Foam technologies, environmental requirements and permitted applications have changed substantially, and the correct extinguishing agent must be selected for the specific hazard and current regulatory requirements.
Frequently Asked Questions
What activates a deluge sprinkler system?
A deluge valve is operated by the system's listed releasing arrangement. On an electrically released system, compatible detection causes the releasing control unit to operate the releasing circuit and associated releasing device.
Are deluge sprinkler heads normally open?
Yes. Conventional deluge systems use open sprinklers or open spray nozzles rather than closed automatic sprinklers with individual heat-responsive operating elements.
Does every deluge sprinkler discharge at once?
Once the deluge valve opens, water is admitted to the system piping and can discharge through the open sprinklers or nozzles supplied by that activated system.
Does a smoke detector always activate a deluge system?
No. Electrically released deluge systems can use detection appropriate for the protected hazard, but not every deluge system is electrically released and smoke detection is not universally appropriate for every application.
Is the solenoid valve the deluge valve?
No. In a typical electrically released arrangement, the solenoid is part of the releasing trim. Its operation allows the deluge valve to open according to the listed valve design.
Can a regular fire alarm panel release a deluge system?
Only equipment and circuits suitable and listed for the required releasing service should be used. A technician should never assume that an ordinary fire alarm output is acceptable merely because its voltage matches the solenoid.
Is deluge the same as dry pipe?
No. A dry pipe system normally uses closed automatic sprinklers and pneumatic pressure in the piping. A deluge system uses open discharge devices and a separate releasing arrangement controlling the deluge valve.
Is deluge the same as preaction?
No. They can use similar valve and releasing equipment, but a preaction system normally uses closed automatic sprinklers. A deluge system uses open sprinklers or nozzles.
Related Fire Sprinkler & Fire Alarm Guides
- Wet Pipe Fire Sprinkler Systems | How They Work
- Dry Pipe Fire Sprinkler Systems | How They Work
- Fire Sprinkler Waterflow Switch | How It Works & Fire Alarm Monitoring
- Waterflow, Backflow, OS&Y and Tamper Switch Basics
Studying for the NICET Fire Alarm Systems Exam?
Releasing systems, initiating devices, output circuits, supervision, alarm signals and sprinkler interfaces are important concepts for fire alarm technicians to understand.
Fire Alarms Online offers a 550-question NICET Fire Alarm Systems practice collection covering Levels I through IV, along with a free 35-question sample.
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Bottom Line
A deluge fire sprinkler system uses open sprinklers or nozzles supplied through a deluge valve. During normal conditions, the valve prevents water from entering the downstream system piping.
When the approved releasing arrangement operates, the deluge valve opens and water is admitted to the system, allowing discharge through the open outlets.
For fire alarm technicians, the critical lesson is understanding the complete chain: detection or other release initiation, control logic, releasing circuit, releasing device, deluge valve operation and actual waterflow or alarm confirmation.
Once those functions are separated, deluge systems stop looking like a mysterious collection of valves, solenoids and wires and start looking like a logical sequence that can be tested and troubleshot one step at a time.
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