Victaulic FireLock NXT 769 Series Installation, Maintenance, And Testing Manual

SECTIONVIEWDRAWINGANDDESCRIPTION–
SERIES776LOW-PRESSUREACTUATOR
The Series 776 Low-Pressure Actuator is located in the trim of Series
769 FireLock NXT Preaction Valves and acts as the trigger for these
systems.
Diaphragms separate the low-pressure actuator into three chambers.
The upper air chamber controls activation, while the middle and lower
chambers act as the water valve.
During setup, system air is applied to the upper chamber of the low-
pressure actuator. When the Auto Vent Sleeve of the low-pressure
actuator is pulled up, the upper chamber manually sets. Air pressure in
the upper chamber holds the Auto Vent closed, while it exerts force on
the water seal of the middle chamber.
When the diaphragm charge line is opened, water enters the lower
chamber of the low-pressure actuator. Water that enters the low-
pressure actuator flows to the middle chamber through the inlet eyelet,
which is pressurized by system air pressure in the upper chamber.
Since the area of the lower diaphragm (exposed to water pressure in
the middle chamber) is greater than the area of the lower chamber, the
lower chamber seals off. Water does not flow to the outlet of the low-
pressure actuator, and the supply water pressure creates the water seal.
When system air pressure decays to 7 psi/0.5 Bar, the force exerted
by the compression spring in the Auto Vent is greater than the force
exerted by air in the upper chamber. The Auto Vent opens, and all air
pressure in the upper chamber evacuates.
The upper diaphragm releases water pressure in the middle chamber
of the low-pressure actuator, which allows the lower diaphragm to lift
and water to flow from the inlet to the outlet. This flow of water releases
pressure from the diaphragm charge line of the Series 769 FireLock
NXT Preaction Valve, thus allowing the diaphragm to retract. The
clapper opens, and water flows into the sprinkler system.
VENT TO ATMOSPHERE
INLET
AIR IN
OUTLET
Illustration is exaggerated for clarity
* Denotes components that can be replaced in the field
Auto Vent Sleeve
Auto Vent Screw
Auto Vent Assembly*
Upper Chamber
Upper Diaphragm Wave Spring
Lower Diaphragm Wave Spring
Outlet Eyelet
Lower Chamber
Lower Diaphragm Assembly
Strainer Screen*
Strainer O-Ring Seal*
Strainer Assembly
Inlet Eyelet
Middle Chamber
Upper Diaphragm Assembly
I-769P.AC/ELEC_8
FireLockNXT™AutoConvertPreactionValve
SERIES 769
PreactionElectricAutoConvertDryTrim
I-769P.AC/ELECINSTALLATION,MAINTENANCE,ANDTESTINGMANUAL
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Victaulic FireLock NXT 769 Series Specifications

General

Brand	Victaulic
Model	FireLock NXT 769 Series
Category	Control Unit
Language	English