Technical data

13.
1.3 Double Interlock Preaction Systems
Double interlock preaction systems are designed to protect water sensitive environments where the inadver-
tent release of water into the protected area will result in serious disruption to critical control systems (e.g.
data centers), and/or serious financial impact to business operations (e.g. freezers). Similar to deluge and
single interlock preaction systems, the double interlock preaction system requires a supplemental detection/
release system that operates independently of the sprinkler system. Double interlock preaction system piping
is pressurized with air or nitrogen, and the pressure is monitored by a pressure switch. In addition to supervis-
ing the integrity of the piping, the pneumatic pressure serves as part of the main system control valve release
sequence.
Double interlock preaction systems provide an extra level of protection against accidental system activation
by requiring that two independent conditions coexist in order for the deluge valve to open. The two events can
be either (a) activation of the electrical detection system and loss of pneumatic pressure in the system piping,
or (b) loss of pneumatic pressure in a dry pilot line and loss of pneumatic pressure in the system piping. It is
important to note that the existence of either condition without the other does NOT result in actuation of the
main system control valve. Operation of the main system control valve occurs only when the two conditions
coexist; when only one condition exists the building owner/occupant can respond (or “preact”) to the condi-
tion and possibly prevent unnecessary release of water into the water sensitive environment.
Figure 11