Technical data

1.2 Single Interlock Preaction Systems
A single interlock preaction system is best described as a dry pipe system that is converted to a wet pipe
system prior to activation of the sprinklers. Unlike deluge systems, preaction systems utilize closed sprinklers
and piping. The closed sprinklers operate individually as needed following the actuation of the main system
control valve. Similar to deluge systems, the single interlock preaction system requires a supplemental detec-
tion/release system that operates independently of the sprinkler system. Single interlock preaction systems
are generally installed to protect water sensitive environments such as computer server rooms, museums,
and hospital operating suites where the inadvertent release of water from a broken sprinkler may result in seri-
ous damage to the contents of the area. Single interlock preaction systems are not subject to the design pen-
alties of dry systems (30% hydraulic remote area increase*, hydraulic calculation C factor of 100, and specific
water delivery requirements), and are therefore appropriate replacements for conventional dry pipe systems.
Single interlock preaction system piping is generally pressurized with air or nitrogen, and is monitored by a
pressure switch that will notify the owner in the event of falling pressure due to sprinkler or pipe damage, or
failure of the compressed gas system. Loss of pneumatic pressure in a single interlock preaction system will
NOT result in actuation of the main system control valve. Operation of the main system control valve occurs
only upon activation of the wet pilot, dry pilot, or electrical release system.
*Note: 30% hydraulic remote area increase is required for preaction systems protecting storage occupancies
governed by Chapter 12 of NFPA 13, Standard for the Installation of Sprinkler Systems.
8.
Figure 6