A dry pipe sprinkler system is a water-based fire protection method that typically installed in spaces subject to freezing conditions and cannot constantly maintain a temperature of at least 40°F. Common installation areas for dry pipe systems include parking garages, cold storage spaces, attics, loading docks, and more. Unlike the water-filled piping in wet pipe systems, dry pipe systems use pipes filled with compressed air. This air holds back water at the dry pipe valve, allowing a low air pressure (20 to 30 psi) to hold back over 100 psi of water pressure.
When fire activates the sprinklers, the air in the dry pipe system is released. As the air discharges, the pressure inside the dry pipe valve drops, causing the valve to open and fill the sprinkler piping with water. This process introduces a delay in water delivery compared to wet systems. NFPA 13 provides requirements for the time needed for the dry valve to open, fill the system with water and deliver water through the activated sprinkler head. To mitigate this delay, quick opening devices are utilized.
NFPA 13 requires dry pipe systems deliver water to the most remote point, known as the inspector’s test connection, within specific times based on the protected occupancy hazard. Some exceptions apply. For example, dry systems with interior piping volume less than 500 gallons do not need to meet these delivery times or have quick-opening devices. For systems up to 750 gallons, if a quick-opening device is installed, it negates the need to meet any delivery time requirements. Systems exceeding 750 gallons are required to meet the times listed in NFPA 13 (2019) Table 8.2.3.6.1.:
In addition to the above times, dry systems protecting dwelling units must deliver water within 15 seconds to each dwelling unit (NFPA 13-8.2.3.6.3).
Quick-opening devices, like exhauster and accelerators, are used to help meet delivery time requirements. Exhausters were mounted on sprinkler piping, where it would sense a drop in the system air pressure and open a larger valve to allow air to escape, thus draining air from the piping more rapidly. Exhausters are no longer manufactured but may be found on older dry sprinkler systems.
Accelerators are mounted to the dry pipe valve itself as part of the trim package. Similar to an exhauster, an accelerator senses a drop in air pressure and will open a larger valve to the dry valve’s intermediate chamber, letting air inside the dry pipe valve escape and equalize with ambient air pressure. While exhausters removed air from the dry sprinkler pipe, accelerators drop the air pressure only within the dry pipe valve itself – reducing the time it takes for water to begin traveling down the pipe towards the open sprinkler(s).
Older accelerators are mechanically operated and tend to be a component that requires a higher level of maintenance throughout the life of a system. One of the traditional issues with mechanical accelerators is that when they are not properly maintained, they will trip when there isn’t a pressure drop in the dry sprinkler system, activating the dry pipe valve and filling the piping with water. These events also tend to activate the dry pipe system’s pressure switch, causing a fire department response.
Newer accelerators are available that utilize electrical components to operate, which sense a pressure drop electronically and activate the valve. These devices tend to be more responsive and far less prone to accidental activation. Electronic accelerators typically have a higher installation cost compared to their mechanical counterparts; however electrical accelerators have been found to have a lower level of maintenance required through the life of the system.
A well-maintained fire protection system is a crucial piece in protecting properties from experiencing loss from fire events. Each component in these systems play a specific role and must be properly maintained to ensure it will operate as intended. Proper maintenance on a system does not necessarily begin once a system has been installed and put in service, it begins with the design and selection of cost-effective, long-lasting components.