How does a Fire Sprinkler work?

Multiple fire sprinkler heads, showing their shapes and sizes

Fire sprinklers are in many commercial and even some residential buildings. Most people know that a sprinkler going off means it’s a bad day and that hanging things off them is probably not the best idea. But how do fire sprinklers work? Does that red pull station by the door turn them on, and we shut them off when the fire is out? There are many misconceptions about fire sprinkler systems. We will provide an outline of the different types of sprinkler systems and how they work. For more detail, contact us, and our team of experts can assist with any questions you may have.

Types of Fire Sprinkler Systems

While the sprinkler heads may mostly look very similar, the system behind them can be quite different. There are four main types of systems, though they all are for the same purpose of putting fires out.

Wet Pipe Systems

Single sprinkler head with sensing element visible
Visible Sensing Element

This is the most common fire sprinkler system that everyone thinks of when they hear of fire sprinklers. All pipes in the system are filled with water and each sprinkler head has a sensing element (fusible link or glass bulb). Should the temperature get too hot at the ceiling, the sensing element will burst and allow for water to flow freely. As the system is filled with water there is minimal delay from activation to system flow. Wet pipe sprinkler systems are the most reliable and cost-effective, though they may not be appropriate for every application. As the water is under pressure in the pipes, the system cannot be subjected to freezing temperatures. Additionally, water can be quite harmful, which may not be appropriate for areas with sensitive equipment.

Dry Pipe Systems

Dry pipe systems are very similar to wet pipe systems. The major difference is that the pipes are filled with air instead of water. This allows for the system to be exposed to freezing temperatures, without any impact to its functionality. Dry systems can be found on patios and canopies, coolers and parking garages, amongst other places. The system is comprised of a specialty valve that keeps the water at bay with the assistance of the air pressure in the system. The sprinkler heads still have a sensing element and upon activation the air will escape. Once enough air has escaped, the valve will open and will release the water into the system and through the sprinkler head. As there is a delay upon activation of a dry pipe system, due to the time it takes to release all the air, the size of dry pipe systems is usually limited.

Preaction Systems

Preaction systems are more specialized systems. Their basic design is quite similar to a dry pipe sprinkler system, though the activation is what differs. Preaction systems are paired with electronic detection devices. A releasing panel is paired with these heat or smoke detectors and is connected to a specialized valve. The pipes of the system are still filled with air, just as they are in the dry pipe system. The sprinkler heads also still contain a sensing element.

There are three sub-types of preaction systems, depending on their activation:
  • Non-interlock system: the system will activate on the operation of detection devices OR if the sensing element of the sprinkler head bursts
  • Single interlock system: the system will ONLY activate on the operation of detection devices
  • Double interlock system: the system will activate if the detection devices AND the sensing element of the sprinkler head bursts.

Detection devices, such as heat detectors, usually have a lower threshold for activation of 135°F (65°C) vs. 165°F (74°C) for sprinkler heads. With a preaction system, multiple criteria can be required before the system will activate. That is the reason it is ideal for museums and other sensitive environments. As the double interlock system will significantly delay activation, with both criteria having to be fulfilled, the same size limits as a dry pipe system apply. Double interlock systems were initially designed for freezer storage warehouses. Areas, where the accidental presence of water can cause a significant amount of damage, are the best candidate for a double interlock.

Deluge Systems

Deluge sprinkler head showing lack of sensing element
Deluge Sprinkler Head Without Sensing Element

Deluge systems are very similar to preaction systems. The deluge system, however, does NOT have sensing elements in the sprinkler heads. That means upon water delivery, the water will flow from ALL sprinkler heads at once. Similar to a preaction system, an electronic means of detection will keep the valve closed. Upon activation of a smoke or heat detector, the system will start flowing water and all sprinkler heads will start releasing. This type of system is most suitable for high-hazard areas, such as power plants or aircraft hangars.

So, How Does a Sprinkler Work?

As you see with the examples above, there are a few different ways a sprinkler system can work. All activations of a sprinkler system are considered automatic, as they do not require any manual input. Most sprinkler systems will activate ONLY where it is necessary, which is usually only one or two sprinkler head locations. That is the reason sprinkler systems are so effective and yet are not as destructive as everyone might think. No matter the sprinkler, the principle is the same. Upon the presence of extreme heat from a fire, the system will activate and start spraying water. Water is one of the best ways to fight the fire, as it attacks the fire in several ways on the tetrahedron. Water cools, removes the heat component, and also removes the oxygen from the fire by displacing it.

Sprinkler System Service

While this article hopefully provided you with a basic outline of sprinkler systems, there are several other components to it. Our team can assist with the design, installation, inspections, and repair of any sprinkler system. We are ready to answer any questions you may have and are ready 24 hours a day, should you encounter any issues with your sprinkler systems.