Fire Sprinkler - Deluge Fire Sprinkler System

A deluge fire sprinkler system works similar to a wet pipe system, however, the deluge system uses open fire sprinkler head or nozzles that do not operate individually.  The pipes are dry in normal operation and the water is held back by an electronic solenoid.  The solenoid is connected and control by a compatible releasing fire control panel.  An initiating device such as a smoke detector or heat detector sends a signal to the releasing panel which in turn energizes the releasing circuit and opens the solenoid.

These types of deluge systems are typically installed in high hazard areas such as power generating stations, aircraft hangers, chemical plants, and other areas that main contain chemicals and or flammable liquids.  Water is not always adequate to control fires in areas where chemicals and flammable liquids are stored.  Often you will find that a foam concentrate is mixed with the water in a part of the system known as the proportioner.  The foam is known as Aqueous Fire Fighting Foam or better known as AFFF.  This foam when mixed with water causes expansion when released through the sprinkler head which in turn deprives the fire of oxygen.

Read more about dry fire sprinkler systems here.

Fire Sprinkler - Dry Pipe Systems

A deluge and pre-action fire sprinkler system are both part of the dry pipe family.  Dry pipe systems are typically installed in areas where water is subject to freezing such as unheated facilities and parking garages.  Unlike the wet pipe fire sprinkler system (filled with water) a dry pipe system is filled with compressed air from a source such as an electric compressor or nitrogen bottle.

Like wet pipe fire sprinkler systems, dry pipe systems also have a valve clapper and alarm port.  The dry pipe valve clapper is held closed by a pressure differential between air pressure and water pressure.  Supervisory pressure switches are typically used to measure the pressure on the system side.  These pressure switches can send either a low or high pressure signal to the panel.  The fire alarm control panel or pre-action panel will then turn on a pump or release pressure depending on the signal (low or high pressure).  This ensures that the correct amount of pressure is present in the system at all times.

In the event of an actual fire and a fire sprinkler head activates, the air pressure in the system is released.  When the air pressure drops to the trip point (usually around 10 psi below normal), the dry pipe valve opens and allows water to flow in from the main source to fill the distribution pipes and out of the activated fire sprinkler head.  Once the water is flowing through the clapper valve, the alarm port is exposed to the water.  At this time a pressure switch senses the increase in pressure and sounds an alarm.

Dry Pipe Valve

A dry pipe valve is located above the main system control valve and must be installed in areas not subject to freezing.  The whole purpose of the dry pipe valve is to ensure water does not enter the distribution piping and freeze.  It is a one way clapper that has a small amount of water covering it known as the priming water.  This priming water helps to seal the valve seat and has an immediate chamber that connects the valve to the alarm line.

Pressure Switches

There are alarm pressure switches and supervisory pressure switches both used in dry pipe fire sprinkler systems.  Both of these pressure switches monitor air pressure on the system side of the dry pipe valve.  The alarm pressure switch measures pressure change within a system and sends alert signals the the main fire control panel or pre-action system panel.  The supervisory air pressure switches monitor air on the system side of the dry pipe valve and perform two different functions.

1.  Monitor low air pressure and prevents accidental operation of the dry pipe valve due to low air pressure from an air compressor failure or leaks in the system.

2.  Monitor high air pressure to prevent damage to the clapper and gaskets in the dry pipe valve.

Fire Sprinkler - Wet Pipe Systems

With fewer components and less installation time, a wet pipe fire sprinkler system is the most common system you will come across.  A wet pipe fire sprinkler system has a series of piping systems or branches that are fed from the main riser.  The term wet pipe system comes from the fact that the fire sprinkler system is always filled with water.  Behind each sprinkler head is water waiting to be released upon activation.  With that said, you will not typically see wet pipe fire sprinkler systems in areas exposed to freezing temperatures such as parking garages, etc.

The operation of a wet pipe fire sprinkler system is rather simple.  The sprinkler heads contain either a fusible glass bulb or metallic heat sensor.  Heat from a fire will cause the fusible glass bulb to burst or the metallic heat sensor to separate which then opens the small valve on the fire sprinkler head causing water from the piping to discharge and extinguish the fire.

Wet pipe fire sprinkler systems are a fixed temperature type installation, meaning each sprinkler head is is activated only if exposed to a predetermined temperature as low as 155 degrees F or as high as 286 degrees F.

Below are three types of wet pipe fire sprinkler systems with additional information on their operation.

Wet pipe fire sprinkler system with and Alarm Check Valve

When water enters the fire sprinkler system it becomes non-potable and unsuitable for drinking.  To keep this water from entering back into the city water system, an alarm check valve is used.  An Alarm Check Valve is a small and simple device consisting of a spring, valve clapper and an alarm port.

Withing the alarm check valve, the spring holds the valve clapper closed allowing water to flow in only one direction.  Once the system is filled, the water remains in the piping until an individual or multiple sprinkler heads are activated.  Once a sprinkler head is activated, water is discharged and needs to be replaced within the piping.  In order for this to happen, the valve clapper opens allowing the water to flow in to the system and out of the activated sprinkler head.  As the alarm port becomes exposed to water pressure, it causes a water motor gong, mechanical horn or audible/visual device to sound.  A more common way to initiate an electric bell or fire alarm horn/strobe, is a water flow device.

To prevent city water surges from causing false alarms, a retard chamber is used.  A retard chamber is a metal reservoir that holds the water during a brief city water surge.  A drip valve at the bottom side of the reservoir allows the water from the surge to slowly drain out.  If a true fire activates a sprinkler head, the drip valve is unable to drain the water fast enough causing the flapper on the water flow device to move thus activating an alarm condition.

Wet pipe fire sprinkler system with Maintained Excess Pressure

In this type of wet pipe fire sprinkler system, excess pressure is pumped in just above the alarm check valve to hold the clapper down even during a city water surge.  This type of wet pip fire sprinkler system eliminates false alarms caused by city water surges.

There are two ways to measure pressure loss in this type of system.

1.  Connect a pressure switch to the system above the alarm check valve.  If as sprinkler head is activated, the pressure switch will detect a loss in pressure and sends an alarm.  Usually a supervisory pressure switch is used to monitor if there are leaks within the system.

2.  Connect a pressure switch to the alarm port on the alarm check valve.  If a sprinkler head is activated, the alarm check valve opens.  When the valve opens, the alarm port is exposed to the incoming water supply.  The pressure switch will detect a change in pressure and will send an alarm.

Wet pipe fire sprinkler system with a straight pipe riser

This type of system will have a straight pipe riser located downstream from the check valve or backflow preventer and are the most common type of wet pipe system.  The vertical supply pipe or riser, does not have a retard chamber or alarm port like others.  Instead you will find a riser check valve.

A riser check valve utilizes a vane type water flow switch to monitor water flowing within the wet pipe fire sprinkler system.  When continuous flow of water equal to 10 gallons per minute occurs, the water flow switch activates an alarm condition after a predetermined amount of time.  This time delay can be selected on the actual water flow device.  This time delay is to help eliminate false alarms caused by city water surges.

NICET Facebook Answers From 4/02/12 - 4/06/12

Okay here are the first two answers from this weeks Facebook group questions.  Make sure to join our Facebook Group to get the questions.

Answer #1:  1 year thereafter


NFPA 72, 2007 edition. 4.5.3.1  A complete record of the tests and operations of each system shall be kept until the next test and for 1 year thereafter.

Answer #2:   4.04 Ohms

NFPA 70, National Electrical Code, 2008 Edition.
Chapter 9, Table 8.
Conductor Properties. #18 AWG Solid Copper Coated = 8.08 Ohms per 1000 feet.
500 / 1000 x 8.08 = 4.04 Ohms.

NICET Facebook Answers From 3/25/12 - 3/30/12

Okay here are the first two answers from this weeks Facebook group questions.  Make sure to join our Facebook Group to get the questions.

Answer #1:  4700 Ohms


Using the standard Resistor Color Code, begin reading the color bands from left to right starting with the band that is nearest to the end of the resistor.
Yellow = 4
Violet = 7
Red = 2 (The 2 indicates that you multiply by 100)
47 x 100 = 4700 Ohms

Answer #2:  Two Detectors or more on each initiating circuit.


NFPA 72, 2007 edition. 10.4.4  Testing Frequency 10.4.4.4.1 Two or more detectors shall be tested on each initiating circuit annually