FireFlex system types: Wet pipe, dry pipe, deluge, and preaction configurations

In general, FireFlex system types fall into four broad categories:

Wet pipe for non-freezing spaces where immediate water discharge is desired
Dry pipe for areas subject to freezing, with standard or high-pressure configurations depending on water supply conditions
Deluge for hazards that require simultaneous discharge through open sprinklers or nozzles
Preaction for water-sensitive areas where water should be kept out of the piping until a specific release sequence occurs

Wet pipe

What it means

A wet pipe system has sprinkler piping that is already filled with water. When a sprinkler opens due to heat, water discharges immediately.

Choose wet pipe when

The protected area is maintained above freezing
You want the simplest and fastest automatic sprinkler operation
There is no need to keep water out of the piping

Why it is commonly selected

Wet pipe systems are often chosen where reliability, simplicity, and immediate discharge are the main priorities.

Dry pipe 175 PSI

What it means

A dry pipe system keeps water out of the sprinkler piping by using supervisory air or gas. Water is held back by a dry pipe valve and enters the system when air pressure drops due to an opened sprinkler. Standard dry pipe versions are rated for conditions up to 175 PSI.

Choose dry pipe 175 PSI when

The protected area may freeze
A standard dry system pressure rating is suitable
The design falls within the system’s standard pressure range

Why it is commonly selected

Dry pipe 175 PSI is typically used in cold environments where piping cannot remain filled with water under normal conditions.

Dry pipe high pressure 250 PSI

What it means

This is a high-pressure dry pipe system designed for water supply conditions up to 250 PSI.

Choose dry pipe high pressure 250 PSI when

Water supply pressure is above the standard 175 PSI range
The project requires a dry pipe solution for higher-pressure conditions
The design team needs a dry system compatible with 250 PSI service

Why it is commonly selected

High-pressure dry pipe configurations are used when freeze protection is needed and the available water supply exceeds standard pressure conditions.

Deluge

What it means

A deluge system uses open sprinklers or nozzles. When the release system operates, the deluge valve opens and water flows through the entire piping network to all open outlets at the same time.

Choose deluge when

Rapid water application over a wide hazard area is required
The hazard needs simultaneous discharge from all nozzles
The risk is high enough that full-area discharge is preferred

Why it is commonly selected

Deluge systems are commonly selected for high-hazard applications where immediate, large-scale water application is part of the fire protection strategy.

Preaction systems

What this system family means

A preaction system is used where accidental water discharge would be a serious problem. Unlike a wet pipe system, the sprinkler piping is normally dry. Water is admitted to the piping only after a defined release event, or combination of events, depending on the interlock arrangement.

Preaction systems are commonly used in water-sensitive areas because they provide added control over when water enters the system piping.

The difference between preaction system types

The difference between non-interlock, single interlock, and double interlock preaction systems is how many events are required before water enters the sprinkler piping.

Preaction non-interlock

What it means

In a non-interlock preaction system, water enters the sprinkler piping when the detection or release condition operates. If the release system does not operate, the system can still operate similarly to a dry system when a sprinkler opens.

This arrangement provides faster piping fill after detection, but it offers less protection against unwanted water entry than the interlocked versions.

Choose non-interlock when

Early system fill is important
You want preaction protection but can accept a lower level of accidental water release protection than interlocked systems
The hazard does not require the added safeguards of single or double interlock

Why it is commonly selected

Non-interlock preaction is often chosen when the design objective is to combine dry-pipe-like operation with faster water delivery following detection.

Preaction single interlock

What it means

In a single interlock preaction system, one release event must occur before water enters the piping. In most applications, that event is a detection signal from the releasing system. Water then fills the piping, but discharge still occurs only through an open sprinkler.

Choose single interlock when

You want better protection against accidental water in the piping than non-interlock
The space is sensitive to water damage
You still want a simpler operating sequence than double interlock

Why it is commonly selected

Single interlock is often the balanced choice for many water-sensitive applications because it adds a safeguard against accidental water entry while maintaining a straightforward sequence of operation.

Preaction double interlock

What it means

In a double interlock preaction system, two events are required before water enters the sprinkler piping:

A detection or release condition
A loss of air pressure caused by an opened sprinkler

This provides the highest level of protection against unwanted water entering the system piping.

Choose double interlock when

Unwanted water release must be minimized
You are protecting highly sensitive spaces such as data rooms, archives, museums, or specialized process areas
The design requires both fire detection and sprinkler operation before water is admitted

Why it is commonly selected

Double interlock systems are commonly selected for applications where preventing unwanted water discharge is critical.

Important note

FireFlex documentation also shows that double interlocked configurations may use electric-pneulectric, electric-pneumatic, or pneumatic-pneumatic release arrangements depending on system design.

Quick selection guide

Wet pipe: simplest operation, immediate discharge, best for non-freezing environments
Dry pipe 175 PSI: for freezing environments with standard pressure conditions
Dry pipe high pressure 250 PSI: for freezing environments with higher water supply pressure
Deluge: for open-nozzle systems requiring simultaneous discharge
Preaction non-interlock: fastest path to filling after detection, with a lower safeguard level against unwanted water entry
Preaction single interlock: balanced choice for many water-sensitive hazards
Preaction double interlock: best choice when minimizing accidental water release is the top priority

How to choose the right FireFlex system type

The correct system type depends on the application, environmental conditions, water supply pressure, hazard profile, and the level of protection needed against accidental water release.

As a practical rule:

Start with environmental conditions: if the space can freeze, consider dry pipe or preaction rather than wet pipe
Consider the hazard response strategy: if the application requires simultaneous discharge, deluge may be appropriate
Consider the sensitivity of the protected space: if water must be kept out of the piping until a controlled release sequence occurs, preaction is often the better fit
Confirm the pressure requirement: where dry systems are needed, verify whether standard 175 PSI or high-pressure 250 PSI conditions apply

For final selection, the system type should always be confirmed against the project design basis, applicable codes and standards, the authority having jurisdiction, hydraulic requirements, and the approved FireFlex configuration for the application.