SECTION VIEW DRAWING AND DESCRIPTION –
SERIES 776 LOW-PRESSURE ACTUATOR
The Series 776 Low-Pressure Actuator is located in the trim of Series
756 FireLock Dry 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 piston 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 pressur-
ized by system air pressure in the upper chamber.
Sin
ce 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 0.4 Bar, the force exerted by the
co
mpression 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 piston charge line of the Series 756 FireLock Dry
Valve, thus allowing the piston to retract. The clapper opens, and water
flows into the sprinkler system.
VENT TO ATMOSPHERE
INLET PORT
(FROM PISTON)
AIR IN
OUTLET PORT
(TO DRAIN)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Exaggerated for Clarity
Bill of Materials
1 Auto Vent Sleeve 9 Lower Diaphragm Assembly
2 Auto Vent Screw 10 Strainer Screen (Replaceable)
3 Auto Vent Assembly 11 Strainer O-Ring Seal
4 Upper Chamber 12 Strainer Assembly
5 Upper Diaphragm Wave Spring 13 Inlet Eyelet
6 Lower Diaphragm Wave Spring 14 Middle Chamber
7 Outlet Eyelet 15 Upper Diaphragm Assembly
8 Lower Chamber
I-756LPA.VDS_6
FireLock
®
European Dry Valve Stations
SERIES 756
WITH SERIES 776 LOW-PRESSURE ACTUATOR
I-756LPA.VDS
INSTALLATION, MAINTENANCE, AND TESTING MANUAL
www.victaulic.com
VICTAULIC IS A REGISTERED TRADEMARK OF VICTAULIC COMPANY. © 2006 VICTAULIC COMPANY. ALL RIGHTS RESERVED. PRINTED IN THE USA.
REV_B
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