Fire Sprinkler Systems

A fire sprinkler system is an active fire suppression system that provides a detection function and automatic dousing of a fire. Sprinkler systems require a constant water pressure supply to ensure correct activation and need to be regularly serviced and tested for correct function in the event of a fire.

There are 4 main types of fire sprinkler systems:

Type 1: Wet Pipe

A wet pipe sprinkler system is a system which constantly has water in the pipes. Because of this it has the fastest reaction time of the four systems. If a fire occurs, the heat will shatter the glass heat-detecting bulb and will result in the water in the pipes immediately dispersing from that sprinkler head to extinguish the fire.

The downfall with this type of system is that the water held in the pipes can freeze if exposed to cold temperatures which can result in a burst pipe and water damage. These are only to be installed in buildings where a consistent temperature of above freezing can be maintained all year round.

Type 2: Dry Pipe

Instead of holding water, a dry pipe sprinkler system works by holding pressured air. The water is supressed in a sprinkler riser by the pressurised air. Once a fire is detected by the glass heat-detecting bulb it will shatter, but before the water can reach it must first allow all of the air to pass. When the bulb breaks there is an imbalance of pressure causing the air to release and the sprinkler riser vale to open allowing the water to flow to the sprinkler head to extinguish the fire.

The air and water pressure must be checked in a dry pipe system on a weekly basis. This is to ensure that the water is able to reach the furthest sprinkler head (from the sprinkler riser) within 60 seconds or less.

Type 3: Deluge

A deluge sprinkler system differs from the above two systems as all of the sprinkler heads are always open. A deluge valve is installed at the beginning of a row of these sprinkler heads which contains the water (or in some cases foam) until required. A detection system is used in conjunction with the sprinkler heads and when they detect heat, smoke or flames (depending on the detectors installed) will send a signal to the deluge valve. The valve will then open and, unlike the wet and dry pipe systems, will discharge water from all of the open sprinkler heads linked to the detector.

This type of system is installed where a high volume of water is needed to supress a fire to prevent the spread e.g. aircraft hangers, power plants, factories, chemical stores etc.

Type 4: Pre-Action (single and double interlock)

A traditional “wet pipe” sprinkler systems gives protection against fires, however it can cause water damage if it is accidently activated in areas with sensitive equipment/stock such as libraries, museums, computer rooms etc. Interlock systems can be installed to allow some time for an alternative extinguishment method (i.e. Fire extinguisher or hose reel) before the sprinkler system is activated.

Single Interlock

Single interlock pre-action systems are generally installed where damage to an automatic sprinkler head or piping (being knocked with a ladder) would result in serious water damage.

The most common places this kind of sprinkler system is installed are libraries, museums, archives etc.

This type of system is used to protect valuable properties where a pre-alarm of a possible fire allows time for an alternative method (portable fire extinguisher or hose reel) before the sprinklers are discharged. If the fire cannot be extinguished then the pre-action sprinklers will then be activated.

Double Interlock

Double interlock pre-action systems are designed for sites where the equipment installed needs maximum protection against the accidental discharge of a sprinkler system such as refrigerated stores, computer rooms etc.

There must be two independent events caused by a fire in order to activate this type of sprinkler system.

There must be a loss of air pressure in the piping due to a sprinkler head being opened and the deluge releasing panel must be energized and open the solenoid valve upon the operation of a fire detection device. This system will only operate when the dry pilot actuator and the solenoid valve are open at the same time.

If just the dry pilot actuator is opened (e.g. a ladder knocks a sprinkler head) or if only the solenoid valve is opened (e.g. misuse or accidental use of an electric manual pull station) an alarm will sound to pre-warn the occupants but the sprinkler system will not activate.

Frequently encountered faults include:

While each system may experience their own individual faults, the most frequently encountered

  • Required maintenance is not regularly attended to.
  • Corrosion
  • Leaking seals
  • Tampered with or knocked sprinkler heads;
  • Missing escutcheon plates.


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