Operation and types of wet pipe sprinkler

Each enclosed spray head is held closed by a heat-sensitive glass bulb or a two-part metal rod held together by a fusible alloy.A glass bulb or linkage holds the pipe cap in place,which acts as a plug to prevent water from flowing unless the ambient temperature around the sprinkler reaches the design activation temperature for the individual sprinkler head.In a standard wet pipe sprinkler system, each sprinkler activates independently when a predetermined heat level is reached.So only the sprinklers that are near the fiery heat will work, usually just one or two.This maximizes water pressure at the point of fire and minimizes water damage to the building.Sprinkler activation typically causes less water damage than fire department hose flow, which provides approximately 900 L/min (250 US gal/min).Typical sprinkler discharges for industrial manufacturing sites are approximately 75–150 L/min (20–40 US gal/min.However, typical Early Suppression Rapid Response (ESFR) sprinklers operate at 50 psi (340 kPa) will discharge approximately 380 L/min (100 US gal/min).Additionally, sprinklers typically activate within one to four minutes of a fire starting, while fire departments typically take at least five minutes to sound the alarm and drive to the fire, and another ten minutes to install equipment and spray spigots on the fire. This extra time can lead to bigger fires that require more water to extinguish.

Types 

Wet pipe

Wet pipe sprinkler systems are installed more frequently than all other types of "fire sprinkler systems".They're also the most reliable because they're simple, with the only operating parts being automatic sprinklers and (usually but not always) automatic alarm check valves.The automatic water supply system provides water under pressure to the system pipes.Wet systems can be optionally charged with antifreeze chemicals for use in situations where piping cannot reliably be maintained above 40 °F (4 °C).While such systems were once common in colder regions U.S.regulators effectively banned new antifreeze installations after the system caught fire due to too much antifreeze.The 2022 sunset date applies to older U.S. antifreeze systems.This regulatory action significantly increased costs and reduced cold weather sprinkler system options.

Dry pipe

Dry pipe systems are the second most common type of sprinkler system.Dry piping systems are installed in spaces where the ambient temperature may be low enough to freeze the water in the wet piping system, making the system inoperable.Dry ductwork is most commonly used in unheated buildings, car parks, external canopies connected to heated buildings (where wet ductwork will also be provided), or refrigerated coolers.In areas using NFPA regulations, wet piping systems cannot be installed unless the ambient temperature range remains above 40 °F (4 °C).Before the system is operational, no water is present in the pipes; instead, the pipes are filled with dry air at a pressure lower than the water supply pressure.To prevent the high water supply pressure from forcing water into the line prematurely, the dry pipe valve (a special type of check valve) is designed by using a larger disc to create greater force at the top of the check valve disc against the Higher water pressure but less disc surface area compared to the area exposed to pipeline air pressure.When one or more automatic sprinklers are triggered, it opens, allowing the air in the ducts to escape from that sprinkler. Each sprinkler operates independently as its temperature rises above its trigger threshold.As the air pressure in the pipe drops, the pressure differential across the dry pipe valve changes, allowing water to enter the pipe system.Water flow from sprinklers needed to control the fire is delayed until air is expelled from the sprinklers.In areas using NFPA 13 regulations, the time it takes water to reach a remote hydraulic sprinkler is limited to a maximum of 60 seconds from the time the sprinkler is activated. In industry practice, this is referred to as "maximum delivery time". Depending on the hazard classification of the area protected by the sprinkler system, the maximum water delivery time may need to be reduced.

• Some homeowners and building occupants may consider dry sprinklers beneficial for protecting valuable collectibles and other water-sensitive areas.This perceived benefit is due to the fear that wet system piping may slowly leak water without being      noticed, whereas dry piping systems should not fail in this manner.

• The disadvantages of using a dry pipe fire sprinkler system include:

• If sprinklers share the same faucet system as that supplying the fire hose, the water supply to the fire hose will be severely reduced or even completely reduced.

• Increased Complexity:Dry piping systems require additional control equipment and air supply components, adding to system complexity.This makes proper maintenance very important, as the added complexity of the system makes the overall      system inherently less reliable (i.e. more single points of failure) compared to wet piping systems.

• Higher installation and maintenance costs: Increased complexity impacts overall dry pipe installation costs and increases maintenance expenditures, primarily due to increased service labor costs.

• Low design flexibility:Regulatory requirements limit the maximum allowable size of a single dry pipe system (ie, 750 gallons) unless additional components and design effort are provided to limit the time from sprinkler activation to discharge to less than 60 seconds.These limitations can increase the number of individual sprinkler zones (i.e., serviced from a single riser) that must      be provided in a building and affect the owner's ability to add systems.

• Increased Fire Response Time:Since the sprinkler operates with the pipe empty,there is an inherent time delay in delivering water to the sprinkler as it flows from the standpipe to the sprinkler, partially filling the pipe process.Regulatory requirements typically allow up to 60 seconds from when an individual sprinkler is turned on until the water is delivered to the fire.This fire suppression delay leads to larger fires before they are contained, increasing property damage.

• Increased Corrosion Potential:Dry sprinkler system piping should be drained after operation or testing,but residual water will collect at low points in the piping and moisture will remain in the atmosphere inside the piping.This moisture, combined with the oxygen in the compressed air in the pipe, can exacerbate corrosion inside the pipe, eventually leading to pinhole leaks or other      pipe failures.Wet piping systems (pipes constantly filled with water) have a much lower rate of internal corrosion because the amount of oxygen available to the corrosion process is more limited.Corrosion can be prevented by using non-corroding copper or stainless steel tubing or by pressurizing the system with dry nitrogen instead of air.Nitrogen generators can be used as a permanent source of nitrogen, which is beneficial because dry-pipe sprinkler systems require an uninterrupted supply of monitored gas.These extra precautions add to the upfront cost of the system, but help prevent system failure, increased maintenance costs, and premature system replacement in the future.