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Nitrogen Generator Short Cycling Prevention Procedure
In situations where the nitrogen generator experiences short cycling, the short cycling is typically the
result of an erratically operating air maintenance device (AMD). Installations where the AMD doesn’t close
properly or partially closes, the nitrogen supply line pressure increases to the cut-out (turn-off) pressure
of the nitrogen generator before the sprinkler systems being supplied are at the proper operating
pressure. Because one or more of the supplied systems did not reach the proper operating pressure when
the nitrogen generator shuts off. The nitrogen supply line depressurizes through the AMD into the
sprinkler system(s). This depressurization allows the supply line pressure to fall below the cut-in (turn-on)
pressure of the nitrogen generator resulting in the nitrogen generator turning on. The process of filling
the nitrogen supply line is repeated.
NOTE: Exacerbated by a small or short nitrogen supply line between the nitrogen generator and sprinkler
system.
Procedure:
1. Increase set point of AMD to prevent premature shut-off of AMD regulator.
2. If set point modifications do not prevent short-cycling, repair (clean out) or replace the erratically
operating AMD.
Air Maintenance Device (AMD) Pressure Adjustment Procedure
The sprinkler system air maintenance device (AMD) operating pressures are determined by the sprinkler
system valve, system water pressure and water delivery time requirements as defined by NFPA 13. The
AMD operating pressures should not need to be readjusted unless one of the above fire sprinkler system
parameters change.
The following procedure has been developed to compensate for:
1. Tolerances of the gauges used on fire sprinkler systems
2. Inlet pressure fluctuations to the AMD resulting in pressure fluctuations of the AMD.
3. Interaction between AMD’s when multiple sprinkler systems are connected to a single nitrogen
generator.
NOTES:
• When the nitrogen generator is connected to multiple dry pipe and preaction systems, the
fire sprinkler systems must operate at the same supervisory gas pressure.
• Any changes to the AMD pressure settings must be correlated with the nitrogen generator
cut-in (turn-on) and cut-out (turn-off) pressure settings; and be authorized by and under the
direction of ECS.
• Accuracy of pressure gauges typically used in the fire sprinkler industry can vary as much as
8-12 psi (.55-.83 bar) (See Operational Information for Sprinkler System Gauge Accuracy).
Determine the operating pressure for all AMD’s connected to a single nitrogen generator. The operating
pressure must be the same for all AMD’s.
NOTE: AMD’s operating at different operating pressures will have an adverse effect on the operation
and can reduce the service life of the nitrogen generator.
Initial Setting of AMD’s
Step 1: Close the valves to all accelerators on the sprinkler systems (if installed).
Step 2: Systems not being checked - Close the all AMD valves.
Step 3: System being checked - Verify the AMD fast fill (bypass) valve is open and the inlet/outlet
(regulated) valves are closed.
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