Ruhrpumpen's Fire Campus: April 2025

When designing a sprinkler system one of the first decisions a designer has to make is what type of sprinkler system should be installed. Types of sprinkler systems permissible by NFPA 13, Standard for the Installation of Sprinkler Systems, are wet, dry, preaction, and deluge. Other types of extinguishing systems, such as clean agent or water mist, are addressed by other standards. When selecting the appropriate sprinkler system type it is important to first understand the differences between the systems and then to understand how these differences can be beneficial, or detrimental, under certain conditions. Selecting the wrong system type can be costly.

Wet Pipe Systems

Wet pipe sprinkler systems are the most common. In this system the sprinkler piping is constantly filled with water. When the temperature at the ceiling gets hot enough the glass bulb or fusible link in a sprinkler will break. Since the system is already filled with water, water is free to flow out of that sprinkler head. Contrary to what Hollywood would have you think, not all sprinkler heads will operate at once in this type of system. The temperature around that specific sprinkler head needs to be high enough to break the glass bulb or fusible link that is holding water back. Once that happens, water will immediately start flowing from only that head.

Wet pipe sprinkler systems are the most reliable and cost effective. Therefore, they should be the first type considered when selecting a sprinkler system. However, there are times when a wet pipe sprinkler system may not be appropriate. One of the major factors in determining if a wet pipe system can be used is the temperature of the space to be protected. Will all areas of the building where the sprinkler piping is

located be conditioned to at least 40OF (4OC) or greater? If the answer is yes, then there is no risk for the water in the piping to freeze and a wet system is the preferred method. However, if the answer is no, an additional study may need to be done to determine if an engineer can prove that although the temperature could drop below 40OF (4OC) it will never drop low enough for the water to freeze. If the temperature of the space cannot be guaranteed to eliminate the risk of freezing water, then a different system type should be chosen.

Source: NFPA 

Dry Pipe Systems

Dry pipe systems are very similar to wet pipe systems with one major difference. The pipe is not constantly filled with water. Instead, the water is held behind a dry pipe valve usually some distance away from where the sprinklers are located. Like a wet pipe system, when the temperature at the ceiling becomes hot enough, the glass bulb or fusible link of the sprinkler breaks. However, in this case, water isn’t immediately available because the pipe is not water filled. Instead, air is released from the now open sprinkler head. This creates a drop in pressure causing the dry pipe valve to open and water to fill the system. Water will then flow from the open sprinkler head. Since there is a delay between sprinkler operation and water flow, the size of dry pipe systems is limited. The size limitation is intended to minimize the amount of time water delivery is delayed.

Source: NFPA

A dry pipe system is a great option for unconditioned spaces, or locations where the temperature of the space cannot be guaranteed to be high enough to prevent water in the system from freezing. It is important to note that a least the portion of the building where the water comes in and the dry pipe valve is located will need to have temperatures hot enough to prevent freezing.

Preaction Systems

Of all the sprinkler system types perhaps the most complicated is the preaction system. There are three different types of preaction systems, a non-interlock system, a single interlock system, and a double interlock system. The main difference between preaction systems and wet and dry pipe systems is that a specific event (or events) must happen before water is released into the system. This might sound similar to a dry pipe system, but the differences lie in what event triggers the release of the water:

· For a non-interlock system: the operation of detection devices OR automatic sprinklers

· For a single interlock system: the operation of detection devices

· For a double interlock system: the operation of detection devices AND automatic sprinklers

Source: NFPA

Deluge Systems

Deluge systems are similar to preaction systems in that they use another type of detection for operation. However, the biggest difference is that deluge systems use open sprinklers or nozzles. Instead of getting water flow from individual heads that have operated, once water fills the system, water will flow from every sprinkler head. Much like a preaction system, a deluge valve will keep water from filling the system until the operation of another type of detection system, such as smoke detection. Once that detection system is activated, water not only fills the system but flows from the open sprinklers or nozzles.

Source: NFPA

Each system type has its own unique benefits. It is important to consider the pros and cons of each system type when selecting which sprinkler system is appropriate for your specific environment.