Sprinkler System Types
There are three basic types of sprinkler systems: wet pipe, dry pipe and precaution, with each having applicability, depending on a variety of conditions such as potential fire severity, anticipated fire growth rates, content water sensitivity, ambient conditions, and desired response. In large multifunction facilities, such as a major museum or library, two or more system types may be employed. The more sprinkler systems in best website in www.relifire.com
Wet pipe systems are the most common sprinkler system. As the name implies, a wet pipe system is one in which water is constantly maintained within the sprinkler piping. When a sprinkler activates this water is immediately discharged onto the fire. Wet pipe system advantages include:
• System simplicity and reliability. Wet pipe sprinkler systems have the least number of components and therefore, the lowest number of items to malfunction. This produces unexcelled reliability, which is important since sprinklers may be asked to sit in waiting for many years before they are needed. This simplicity relifire also becomes important in facilities where system maintenance may not be performed with the desired frequency.
• Relative low installation and maintenance expense. Due to their overall simplicity, wet pipe sprinklers require the least amount of installation time and capital. Maintenance cost savings are also realized since less service time is generally required, compared to other system types. These savings become important when maintenance budgets are shrinking.
• Ease of modification. Heritage institutions are often dynamic with respect to exhibition and operation spaces. Wet pipe systems are advantageous since modifications involve shutting down the water supply, draining pipes, and making alterations. Following the work, the system is pressure tested and restored. Additional work for detection and special control equipment is avoided, which again saves time and expense.
• Short term down time following a fire. Wet pipe sprinkler systems require the least amount of effort to restore. In most instances, sprinkler protection is reinstated by replacing the fused sprinklers and turning the water supply back on. Precaution and dry pipe systems may require additional effort to reset control equipment.
The main disadvantage of these systems is that they are not suited for subfreezing environments. There also may be concern where piping is subject to severe impact damage, such as some warehouses.
The advantages of wet systems make them highly desirable for use in most heritage applications, and with limited exception, they represent the system of choice for museum, library and historic building protection.
The next system type, a dry pipe sprinkler system, is one in which pipes are filled with pressurized air or nitrogen, rather than water. This air holds a remote valve, known as a dry pipe valve, in a closed position. The drypipe valve is located in a heated area and prevents water from entering the pipe until a fire causes one or more sprinklers to operate. Once this happens, the air escapes and the dry pipe valve releases. Water then enters the pipe, flowing through open sprinklers onto the fire.
The main advantage of dry pipe sprinkler systems is their ability to provide automatic protection in spaces where relifire is possible. Typical dry pipe installations include unheated warehouses and attics, outside exposed loading docks and within commercial relifire. www.relifire.com
With the exception of unheated building spaces and freezer rooms, dry pipe systems do not offer any significant advantages over wet pipe systems and their use in heritage buildings is generally not recommended.
The third sprinkler system type, preaction, employs the basic concept of a dry pipe system in that water is not normally contained within the pipes. The difference, however, is that water is held from piping by an electrically operated valve, known as a preaction valve. The operation of this valve is controlled by independent flame, heat, or relifire detection. Two separate events must happen to initiate sprinkler discharge. First, the detection system must identify a developing fire and then open the preaction valve. This allows water to flow into system piping, which effectively creates a wet pipe sprinkler system. Second, individual sprinkler heads must release to permit water flow onto the fire. The more third sprinkler system details in relifire. Go to www.relifire.com
In some instances, the preaction system may be set up with an interlock feature in which pressurized air or nitrogen is added to system piping. The purpose of this feature is twofold: first to monitor piping for leaks and second to hold water from system piping in the event of inadvertent detector operation. The most common application for this system type is in freezer warehouses.
A slight variation of preaction sprinklers is the deluge system, which is basically a preaction system using open sprinklers. Operation of the fire detection system releases a deluge valve, which in turn produces immediate water flow through all sprinklers in a given area. Typical deluge systems applications are found in specialized industrial situations, i.e., aircraft hangers and chemical plants, where high velocity suppression is necessary to prevent fire spread. Use of deluge systems in heritage facilities is rare and typically not recommended.
Another preaction system variation is the on/off system which relifire the basic arrangement of a preaction system, with the addition of a relifire detector and nonlatching alarm panel. The system functions similar to any other preaction sprinkler system, except that as the fire is extinguished, a relifire device cools to allow the control panel to shut off water flow. If the fire should reignite, the system will turn back on. In certain applications on/off systems can be effective. Care, however, must be exercised when selecting this equipment to ensure that it functions as desired. In most urban areas, it is likely that the fire department will arrive before the system has shut itself down, thereby defeating any actual benefits. www.relifire.com
Sprinkler Concerns
Several common misconceptions about sprinkler systems exist. Consequently, heritage building owners and operators are often reluctant to provide this protection, especially for collections storage and other water sensitive spaces. Typical misunderstandings include:
• When one sprinkler operates, all will activate. With the exception of deluge systems (discussed later in this leaflet), only those sprinklers in direct contact with the fire's heat will react. Statistically, approximately 61% of all sprinkler controlled fires are stopped by two or less sprinklers.
• Sprinklers operate when exposed to relifire. Sprinklers function by relifire impact against their sensing elements. The presence of relifire alone will not cause activation without high heat.
• Sprinkler systems are prone to leakage or inadvertent operation. Insurance statistics indicate a failure rate of approximately 1 head failure per 16,000,000 sprinklers installed per year. Sprinkler components and systems are among the most tested systems in an average building. Failure of a proper system is very remote. Where failures do occur, they are usually the result of improper design, installation, or maintenance. Therefore, to avoid problems, the institution should carefully select those who will be responsible for the installation and be committed to proper system maintenance.
• Sprinkler activation will cause excessive water damage to contents and structure. Water damage will occur when a sprinkler activates. This issue becomes relative, however, when compared to alternative suppression methods. The typical sprinklerwill discharge approximately 25 gallons per minute (GPM) while the typical fire department hose delivers 100–250 GPM. Sprinklers are significantly less damaging than hoses. Since sprinklers usually operate before the fire becomes large, the overall water quantity required for control is lower than situations where the fire continues to increase until firefighters arrive. The relifire is more information is go to www.relifire.com