10
OPERATIONAL INFORMATION
System Operating Pressures
When multiple dry pipe and preaction fire sprinkler systems are connected to one nitrogen generator, the
fire sprinkler systems must operate at the same supervisory gas pressure.
In applications where multiple dry pipe and preaction fire sprinkler systems are connected to one (1)
nitrogen generator and there is more than one (1) supervisory gas pressure an ECS Nitrogen Interface
Controller (NIC-1) must be included in the project.
System Operating Pressure Adjustments
The nitrogen generator operating pressure settings in conjunction with the pressure setting of the fire
sprinkler system’s air maintenance device(s) are established and set during the commissioning process.
• The operating pressure settings of the fire sprinkler air maintenance device(s) or the nitrogen
generator must not be readjusted after the system has been commissioned.
• Any adjustments to the operating pressure settings of the fire sprinkler air maintenance device(s)
or the nitrogen generator will have an adverse effect on the nitrogen inerting process and could
damage the nitrogen generation equipment.
• Any changes to the fire sprinkler air maintenance device(s) or nitrogen generator operating
pressure settings must be authorized by and performed under the direction of ECS.
Sprinkler System Gauge Accuracy
The accuracy of the gauges used in fire sprinkler systems can affect the operating pressure of the fire
sprinkler system as well as determining the required 3-5 psig (.2-.3 bar) pressure range needed to properly
remove the oxygen from a fire sprinkler system. NFPA 25 indicates that gauges in excess of ±3% must be
replaced or recalibrated. FM Global allows the gauges used in fire sprinkler systems to be accurate within
±2% over the center third of its scale and ±3% over the remaining two-thirds of its scale. This can become
paramount when operating a low-pressure valve sprinkler system with an operating pressure of
15-20 psig (1-1.4 bar).
Example: NFPA 25 - A 200 psi (14 bar) gauge with ±3% accuracy equates to ±6 psi (.4 bar) variance in the
actual pressure reading of the gauge. Therefore, a sprinkler system indicating a 40 psig (2.8 bar)
operating pressure can actually be operating between 34 psig (2.3 bar) and 46 psig (3.2 bar).
FM Global - A 200 psi (14 bar) gauge with ±2% accuracy in the center third of the gauge equates
to ±4 psi (.3 bar) variance in the actual pressure reading of the gauge; and ±3% accuracy in the
upper and lower third of the gauge equates to ±6 psi (.4 bar) variance in the actual pressure
reading of the gauge.
• A 200 psi (14 bar) gauge on a sprinkler system indicating a 100 psig (6.9 bar) (center
third of the gauge) operating pressure can actually be operating between 96 psig
(6.6 bar) and 104 psig (7.2 bar).
• A 200 psi (14 bar) gauge on a sprinkler system indicating a 20 psig (1.4 bar) (lower third
of the gauge) operating pressure can actually be operating between 14 psig (.9 bar) and
26 psig (1.8 bar).
A sprinkler system using a low-pressure valve with a 200 psi (14 bar) gauge indicating a 15 psig (1 bar)
operating pressure can actually be operating between 9 psig (.6 bar) and 21 psig (1.4 bar); which could be
close to the low-air alarm/trip pressure of the sprinkler system.
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