How do dry sprinkler systems work

SPRINKLER SYSTEMS

What types of sprinklers are there, how do the systems work and where are they used?

Wet system:

In a wet system, the pipe network upstream and downstream of the valve station is constantly filled with water and is under pressure. If the first sprinkler is triggered in the event of a fire, water immediately flows out of the nozzle. The alarm valve station acts like a non-return valve. A drop in pressure above the valve flap opens it and existing extinguishing water can flow into the sprinkler pipe network. A wet system may only be installed if there is no risk of frost.

Drying system:

In a dry system, the sprinkler pipe network is only filled with water from the pump to the alarm valve station. After the valve station, the lines are filled with compressed gas, which instead of water keeps the alarm valve closed. In the event of a fire, the sprinkler opens, the compressed air escapes and the extinguishing water flows in. Drying systems are used when there is a risk of frost (e.g. in underground garages, outdoor warehouses) or when extremely high temperatures would evaporate the extinguishing water.

Tandem system:

A tandem system is a combination of a wet and a dry system. The system makes sense when a small part of the protected area is at risk of frost, but a separate drying system would not be worthwhile. The dry system draws its extinguishing water from the sprinkler pipe network of the wet system. This means that there are no additional costs for a separate water supply.

Rapid drying system:

A rapid drying system is installed when there is a risk of frost and a very high burn rate must be expected. In contrast to a normal drying system, the dry alarm valve is opened by a fire alarm system. This triggers an early alarm message. The sprinkler pipe network is filled with water before a sprinkler head responds.

Pre-action system:

A pre-action system has a similar structure to a drying system. They are also called pilot-controlled drying systems. It is used in sensitive areas in which an unintentional escape of extinguishing water, e.g. through damage to a sprinkler, must be avoided. The main difference: in the event of a fire, only the fire alarm system can open the valve. In order to monitor the pipeline network, the sprinkler pipe network is under pressure. In the event of mechanical sprinkler damage, there is a sudden drop in pressure, which in turn triggers an alarm signal. However, no extinguishing water enters the sprinkler pipe network because the fire alarm system has not reported an alarm and the dry alarm valve has not been opened.

How do you clean sprinkler systems?

Regular cleaning is essential to guarantee the functional reliability of a sprinkler system. If rust particles or other deposits have clogged nozzles and lines, nothing works at all in an emergency. If rust has built up in the pipes, strong acids (e.g. hydrochloric acid) are often used to remove them. Unfortunately, these acids also damage the healthy pipe at the same time and, in case of doubt, can also damage the sprinkler nozzles. That would mean a total failure of the system. For this reason, strong acids should never be used for derusting, but rather products that do not dissolve the rust, but only detach, disperse and rinse out.

Which standards apply to sprinkler systems?

DIN EN 12845:

Regulates the planning, installation and maintenance of fixed fire fighting systems and automatic sprinkler systems

DIN EN 14489:

The draft standard regulates the requirements for the use of sprinkler systems on the basis of DIN EN 12845 and shows general principles

VdS CEA 4001:

Sprinkler system VdS

Guidelines for planning and installing sprinkler systems

At what intervals do sprinkler systems have to be checked?

The state building regulations, the workplace and industrial safety regulations require the operators of commercial and industrial companies to ensure that fire protection measures are in place. This also includes the professional installation of extinguishing systems and their regular maintenance.

Continuous controls ensure that the operational readiness of the systems is maintained and that they function reliably in an emergency.

Among other things, the operator must carry out the following inspections on the stationary extinguishing systems (detailed list in VdS 2091 and 2893):

  • Daily visual checks
  • Weekly checks
  • Monthly checks
  • Semi-annual and annual maintenance
  • 25 year review / 12.5 year review