page_title: Fire sprinkler system
section_title: Dry pipe systems
hierarchical_section_title: Fire sprinkler system / Types / Dry pipe systems
caption_attribution_description: English: Dry pipe system 6 in. supply main with corrosion debris caused by oxidation of steel piping
context_page_description: A fire sprinkler system is an active fire protection method, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected. Although historically only used in factories and large commercial buildings, systems for homes and small buildings are now available at a cost-effective price. Fire sprinkler systems are extensively used worldwide, with over 40 million sprinkler heads fitted each year. In buildings completely protected by fire sprinkler systems, over 96% of fires were controlled by fire sprinklers alone.
context_section_description: Dry pipe systems are the second most common sprinkler system type. Dry pipe systems are installed in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable. Dry pipe systems are most often used in unheated buildings, in parking garages, in outside canopies attached to heated buildings (in which a wet pipe system would be provided), or in refrigerated coolers. In regions using NFPA regulations, wet pipe systems cannot be installed unless the range of ambient temperatures remains above 40 °F (4 °C).
  Water is not present in the piping until the system operates; instead, the piping is filled with air at a pressure below the water supply pressure. To prevent the larger water supply pressure from prematurely forcing water into the piping, the design of the dry pipe valve (a specialized type of check valve) results in a greater force on top of the check valve clapper by the use of a larger valve clapper area exposed to the piping air pressure, as compared to the higher water pressure but smaller clapper surface area.
  When one or more of the automatic sprinkler heads is triggered, it opens allowing the air in the piping to vent from that sprinkler. Each sprinkler operates independently, as its temperature rises above its triggering threshold. As the air pressure in the piping drops, the pressure differential across the dry pipe valve changes, allowing water to enter the piping system. Water flow from sprinklers, needed to control the fire, is delayed until the air is vented from the sprinklers. In regions using NFPA 13 regulations, the time it takes water to reach the hydraulically remote sprinkler from the time that sprinkler is activated is limited to a maximum of 60 seconds.  In industry practice, this is known as the "Maximum Time of Water Delivery". The maximum time of water delivery may be required to be reduced, depending on the hazard classification of the area protected by the sprinkler system.
  Some property owners and building occupants may view dry pipe sprinklers as advantageous for protection of valuable collections and other water sensitive areas. This perceived benefit is due to a fear that wet system piping may slowly leak water without attracting notice, while dry pipe systems may not fail in this manner.
  Disadvantages of using dry pipe fire sprinkler systems include:
  If the sprinklers share the same standpipe system as the standpipe system which supplies fire hoses, then the water supply to the fire hoses would be severely reduced or even curtailed altogether.
  Increased complexity: Dry pipe systems require additional control equipment and air pressure supply components which increases system complexity. This puts a premium on proper maintenance, as this increase in system complexity results in an inherently less reliable overall system (i.e. more single failure points) as compared to a wet pipe system.
  Higher installation and maintenance costs: The added complexity impacts the overall dry-pipe installation cost, and increases maintenance expenditure primarily due to added service labor costs.
  Lower design flexibility: Regulatory requirements limit the maximum permitted size (i.e. 750 gallons) of individual dry-pipe systems, unless additional components and design efforts are provided to limit the time from sprinkler activation to water discharge to under one minute. These limitations may increase the number of individual sprinkler zones (i.e. served from a single riser) that must be provided in the building, and impact the ability of an owner to make system additions.
  Increased fire response time: Because the piping is empty at the time the sprinkler operates, there is an inherent time delay in delivering water to the sprinklers which have operated while the water travels from the riser to the sprinkler, partially filling the piping in the process. A maximum of 60 seconds is normally allowed by regulatory requirements from the time a single sprinkler opens until water is discharged onto the fire. This delay in fire suppression results
caption: Dry pipe sprinkler system supply main with corrosion debris caused by oxidation
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