Get Your Feet Wet in Sprinkler System Basics

Familiarize yourself with some specialized suppression systems.

Most if not all commercial and multifamily or occupant residential structures that are built today have an automatic fire sprinkler system installed. The purpose of these systems is to provide containment of a fire until emergency forces can arrive to extinguish it. Unlike Hollywood portrays, however, all of the sprinklers do not activate when a manual station is pulled or a smoke detector is activated.

As installers of fire alarm systems, we interface with these systems on a daily basis, both in the installation of new systems and in the testing and inspection of existing systems. Depending on the state or jurisdiction that you are working in, you may or may not be allowed to perform any of the associated alarm work on a sprinkler system.

I have found that with most new buildings, the sprinkler contractor will install the flow or alarm pressure switch as well as the valve supervisory switches. This just leaves the final terminations and testing. Forty-plus years ago when I started in the industry it was the alarm company that installed all of the alarm and supervisory devices.

4 Common Sprinkler Systems to Consider
There are four basic types of sprinkler systems that are installed: wet pipe, dry pipe, pre-action and deluge. Let’s take a brief look at what each entails.
Wet Pipe – This is the most common type of sprinkler system system, in which there is water in the piping system throughout the building. When a sprinkler fuses, within a few seconds water will start to flow out and onto the fire.

Dry Pipe – Just as the name implies, there is no water in the branch piping within the building. The water is held behind the alarm check valve. The piping is kept at a slight positive pressure. This keeps the alarm check valve in the closed position. When a sprinkler is fused, there will be a rush of air being expressed. This will lower the pressure of the system and will allow the alarm check valve to open.

At this time water will begin to flow into the branch piping and within a few moments flow out of the fused sprinkler. Within these systems there will generally be a small air compressor, which is set to activate when the pressure within the branch piping drops below a set level.

A dry pipe system may be found in a freezer or in conjunction with sprinklers that are located on the outside of a building in areas prone to freezing temperatures.

Pre-action – This is basically a dry pipe system with additional features. The system may be either of a single or double interlock configuration. One highlight of a pre-action system is that it enlists automatic fire detection devices. Depending on the system, these detectors may be cross-zoned.
With a single interlock system, the alarm check valve will be opened upon the activation of the detection system. At this time, water should flow into the branch lines. Water will not be released, however, until a sprinkler fuses.

A double interlock system requires both the activation of the detection system and the fusing of a sprinkler before the alarm valve will be released.

Pre-action systems are found in areas in which the building owner or occupants wish to avoid the release of water unless there is a fire, as much as it can be verified by automatic means. Venues such as laboratories, libraries and museums are likely candidates.

Deluge – As the name of this final type suggests, when a deluge system is actuated there is a rapid flow of water through all of the sprinklers.
In this one case, the representation made by Hollywood is accurate; things can get very wet as you’d imagine. All of the sprinklers are open, so there is no fusing. Activation of a deluge system typically occurs through the tripping of a manual station.

Make Sure You Know What You’re Testing It is important to know and understand which kind of sprinkler system you are working with, as the type of alarm equipment and testing requirements vary. While a vane flow switch may be used on a wet pipe system, for instance, only a pressure switch may be used on the dry pipe, pre-action and deluge. This is because the pressure of the water flowing into the branch lines through the main riser might be enough to dislodge the vane from a vane flow switch. This could cause a blockage.

While one does use an inspector’s test valve (ITV) for the testing of a wet pipe system, without precautions, opening the ITV on a dry or pre-action may have negative repercussions. The tripping of a deluge system could produce a very wet event in a space where that should not be occurring … leading to a very unhappy customer.

In the August issue I will follow up by detailing several of the specialized sprinkler systems that you may come across.

About the Author

Contact:

Shane Clary, Ph.D., is Security Sales & Integration’s “Fire Side Chat” columnist. He has more than 37 years of security and fire alarm industry experience. He serves on a number of NFPA technical committees, and is vice president of Codes and Standards Compliance for Pancheco, Calif.-based Bay Alarm Co.

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