What Types of Sprinkler Systems Exist?

MeyerFire University | FX105.01

By Franck Orset

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What types of sprinkler systems exist?  

WET SPRINKLER SYSTEM

There are principally four different types of fire sprinkler systems we use today. They are wet-pipe, dry-pipe, pre-action, and deluge systems. 

The most common, and probably the most reliable, system is the wet-pipe sprinkler system, or commonly a “wet system”.  

International standards for the installation of these systems has been available for more than 100 years and large return on experience demonstrated its reliability over the time, when adequately designed and maintained, of course.  

INTERNATIONAL STANDARDS

International standards for the installation of these systems has been available for more than 100 years and large return on experience demonstrated its reliability over the time, when adequately designed and maintained, of course.  

WET SYSTEM WORKINGS

This system consists of pipe which is full of water at all times. These wet-pipe sprinkler systems use closed sprinklers, or sprinklers that are plugged with a heat element, that will only operate once that heat element reaches a given temperature.  

During a fire, the heat from the fire source rises to the ceiling level. This hot smoke layer from the fire reaches the nearest sprinkler, and begins to warm the sprinkler’s heat element. Once the fusible link or glass bulb reaches its appropriate temperature, it breaks and releases the plug of the sprinkler. With the plug release, water discharges from the sprinkler into a specific spray pattern that cools and wets the flame.  

WET SYSTEM ADVANTAGES

Wet systems have a few advantages. 

We already mentioned they can be more reliable. Less mechanical and electrical components allows the reliability of these systems to remain high.  

Since the system is already filled with water, there is no delay in water being released from the sprinkler once the sprinkler activates. Water is ready to go right at the sprinkler itself.  

Wet systems also corrode less than dry pipe or pre-action systems. Once they are charged with water initially, they don’t get any new oxygen inside the system. Corrosion needs both water molecules and oxygen to oxidate, so without new oxygen, corrosion is limited on the inside of the pipe wall. 

Wet systems are less expensive than other systems.  

Dry and pre-action systems require more complex valve equipment and air compression equipment. They require pipe to be sloped.  

They also require more taxing hydraulic calculations, because a dry system inherently has to fight a larger fire due to the time delay of water arriving at the source. 

Wet systems also have more options on configuration. They can be a tree system, a looped system, or a gridded system. The later two provide redundant pathways for water to flow, which adds to reliability and cuts down on friction loss in the system. This makes for a more efficient system overall, and often a less expensive system since pipe sizes can become smaller. 

DRY PIPE SPRINKLER SYSTEM

The dry pipe sprinkler system is a derivation from the wet sprinkler systems for environments exposed to freezing.  

This could be outdoor environments in colder climates, or it could be within interior spaces such as coolers and freezers.  

For a dry system, the pipe network is filled with air, or as is becoming more common now, just with nitrogen. For a dry system, the water supply, dry valve, and its equipment still need to be in a heated environment so the components won’t freeze. 

The positives for using a wet system are conversely the negatives with a dry system. As compared to wet systems, dry systems are more costly, they have less options on configuration, are required to be sloped, corrode quicker, have more friction loss hydraulically, have more demanding calculation needs, can only be used with certain types of pendent and sidewall sprinklers, and require remote inspector’s tests.  

We’ll get into this in a lot more detail later. 

Dry systems are not bad – they’re just more complex than their wet system counterpart. 

ALTERNATIVE SPRINKLER SYSTEM

An alternative sprinkler system is a mix between wet and dry pipe systems. They are not allowed in the United States but were very common in Europe a few years ago.  

These systems are dry pipe systems during cold weather conditions, and because dry pipe systems have a longer activation delay, they are put in a wet pipe mode during the hot season. The obvious issue resulting from this operation is corrosion. Such systems needed replacement and presented serious maintenance issues after just a few years of operation. The introduction and removal of water introduces new water and oxygen molecules, which provide ample fuel for corrosion on the interior of the system. 

As these systems were designed to be dry, there was no reason to consider that a fire that could be controlled during the wintertime would not be controlled during the summertime. If you find these types of systems, it is highly recommended to keep them dry all time to help reduce corrosion. 

ALTERNATIVE SPRINKLER SYSTEM

Aside from wet and dry systems, some sprinkler systems use an antifreeze solution. This could be a derivation from a wet system, to protect an area exposed to freezing conditions, such as a canopy, or could make up an entire sprinkler system.  

For small systems, the antifreeze solution is checked on a regular basis to check its homogeneity. For large antifreeze systems, a tank containing antifreeze solution and a circulation pump may be necessary to maintain the homogeneity of the antifreeze solution.  

Antifreeze systems have limitations and more frequent maintenance needs than wet systems do. Homogeneity of the solution is critical, as tragic fire incidents have shown. The antifreeze solution itself can be flammable if the concentration is too high, which obviously works against the goal of a fire suppression system. 

The requirements surrounding antifreeze systems have changed regularly in the past decade, and will likely continue to adjust as we develop new products and testing now knowing the importance of a well mixed antifreeze solution. 

PREACTION SYSTEMS

A preaction sprinkler system is a another type of sprinkler system. It combines some of the advantages of a wet sprinkler system with the freeze resistance of dry pipe systems. 

Pre-action systems are normally filled with air or nitrogen. These systems have detectors other than sprinklers which are more sensitive than sprinklers. When these detectors activate, the pre-action system fills the network with water so that water is ready to go when the sprinkler itself activates. 

These separate detectors are often smoke detectors, which tend to be more sensitive and activate earlier than sprinklers. 

Pre-action systems are often used in areas where sensitive equipment are located and where the activation of a wet sprinkler system could create serious damages, such as computer or server rooms. They can also be used in large freezer storage, where just the introduction of water for any reason other than a fire could be problematic.

Pre-action systems have three variations. Non-interlock, single-interlock, and double-interlock.  

TYPES OF PREACTION SPRINKLERS

A non-interlock pre-action system requires the activation of a detector or a sprinkler to allow water into the pipe network. If the detector is a smoke detector, then smoke to the detector or sprinkler activation would allow water to flow into the system. These systems are considered to be more ‘fail-safe’, since they are designed to still work even if the detection system were to fail. 

A single-interlock preaction system is set-up so that water is introduced to the system upon operation of a detector, such as a smoke detector. Once a smoke detector activates, it opens an automatic valve that introduces water to the pipe network.  

A double-interlock preaction system is a little different. It requires both a detector to operate, such as a smoke detector, and a sprinkler to activate, just to introduce water into the system. Double interlock pre-action systems have greater limitations and require similar hydraulic hurdles as dry-pipe sprinkler systems, because water is delayed in getting to the fire once a sprinkler activates.  

DELUGE SYSTEMS

Last, a deluge system is our last type of sprinkler system. In a deluge system, all of the sprinklers have open orifices. There is no air pressure maintained on the network.  

Water in a deluge system is held by an automatic control valve, or a deluge valve, and water is charged into the system when a detector activates and opens the deluge valve in the event of a fire. Deluge valves permit large amounts of water to flow across a specific area, and are used for quick-expanding fires, three-dimensional hazards, exterior hazards, or special hazard systems.  

WINDOW SPRINKLERS

One note here is that the term “window curtain wall” or “window sprinklers” sometimes get confused with “deluge” sprinkler systems. Sprinklers directed at windows or spaced to protect an opening are usually closed-sprinklers connected to a wet system and operate like a traditional sprinkler, just with a different objective. A “deluge” sprinkler system is a specific type of system with open sprinklers, a detection system, and a deluge valve to release the water. 

In summary, there are four principle types of sprinkler system, with some deviations. Wet-pipe, dry-pipe, pre-action, and deluge make up our four principal types of systems. We’ll get into more detail on each of these in future videos.  

I am Franck Orset, this is MeyerFire University.