Sprinklers

Dry Sprinkler Systems

   In a dry-pipe system, sprinklers are attached to pipes that contain pressurized air. When heat activates the sprinklers, the air pressure is reduced, allowing the dry-pipe valve to open (or trip) and water to flow to the sprinklers.
Dry-pipe systems are usually used only when temperatures are not high enough to prevent freezing (Below 40 deg. F).
Since dry systems have a slower response time, they should be converted to wet-pipe systems as soon as sufficient heat becomes available.
In situations where only a few sections lack heat, it is recommended to use a combination of dry and wet-pipe systems.

Wet Sprinkler Systems

   The sprinklers in these systems are attached to pipes containing pressurized water at all times. Individual sprinklers in the vicinity of a fire are set off by heat, allowing water to flow through them immediately.
Wet-pipe systems are used wherever temperatures are high enough to prevent freezing.
When water freezes it expands.  Burst pipes may render a system inoperable and can cause significant water damage.
Sometimes, an anti-freeze solution is added to certain sections in a wet-pipe system to prevent freezing.

Deluge Sprinkler Systems

   In these systems, sprinklers are open at all times. They are connected to a dry pipe that is connected to a main water supply.
A fire detection device controls the main valve. When it is activated, the valve opens, allowing large amounts of water to flow through all of the sprinklers.
The purpose of a deluge system is to quickly wet down an entire hazard area to prevent a fire from spreading. They are usually used in facilities that contain hazardous materials such as: flammable liquids, chemicals, and explosives. Rooms with high ceilings sometimes use deluge systems, as it is difficult to direct water over the burning area from such a distance.

 

Fire Pumps

   Fire pumps are needed when the local municipal water system cannot provide sufficient pressure to meet the hydraulic design requirements of the fire sprinkler system. This usually occurs if the building is very tall, such as in high-rise buildings, or in systems which require a relatively high terminal pressure at the fire sprinkler in order to flow a large volume of water, such as in storage warehouses. Fire pumps are also needed if fire protection water supply is provided from a ground level water storage tank.

Fire pumps may be powered either by an electric motor or a diesel engine, or, very occasionally a steam turbine. If the local building code requires power independent of the local electric power grid, a pump using an electric motor may utilize, when connected via a listed transfer switch, the installation of an emergency generator.
The fire pump starts when the pressure in the fire sprinkler system drops below a threshold. The sprinkler system pressure drops significantly when one or more fire sprinklers are exposed to heat above their design temperature, and opens, releasing water or alternatively when other firefighting connections are opened, causing a pressure drop.
Types of pumps used for fire service include: horizontal split case, vertical split case, vertical inline, vertical turbine, and end suction.
A jockey pump is a small pump connected to a fire sprinkler system in parallel with the fire pump. It maintains pressure in a fire protection piping system to an artificially high level so that the operation of a single fire sprinkler will cause an appreciable pressure drop which will be easily sensed by the fire pump automatic controller, causing the fire pump to start. The jockey pump is essentially a portion of the fire pump’s control system. The main code that governs fire pump installations in North America is the National Fire Protection Association’s (NFPA) NFPA 20 Standard for the Installation of Stationary Fire Pumps for Fire Protection.

Source: http://en.wikipedia.org/wiki/Fire_pump

Anti-Freeze Loops

   Anti-freeze loops protect areas in a building or outside a building that are prone to freezing. A check valve isolates the anti-freeze loop from the rest of the sprinkler system. There is also a main drain and a fill cup to assist in the draining and refilling of the loop. Anti-freeze loops are filled with a variety of different liquids, the most common being: propylene glycol, glycerin and ethylene glycol.

If the sprinkler system is connected to a public water supply, ethylene glycol should not be used. Also, systems that are constructed out of CPVC plastic pipe should only be filled with glycerine. NFPA requires the testing of antifreeze loops on an annual basis.  AFP tests the anti-freeze solution with an refractometer to ensure that the solution will stand up to freezing temperatures.

 

Pre-Action Sprinkler Systems

   These systems contain an additional fire-detection device that will recognize a fire before the sprinklers are activated. The sprinklers are attached to a pipe containing air that may or may not be pressurized.
When the detection device senses a fire, it opens the main valve, allowing water to flow through the pipes before the sprinklers are set off. When the heat activates the sprinklers, water flows through immediately, as in a wet-pipe system.
Pre-action systems are usually employed in areas that are at risk for serious water damage due to damaged sprinkles and/or piping.
They operate faster than dry systems, but tend to be significantly more expensive.