At the heart of Reliable’s Single Interlock Preaction System is the
Model EX Valve. This valve is a hydraulically operated, straight-
through-design, differential-type valve (see Fig. 2). System
maintenance is simplied since priming water is not required and the
deluge valve can be reset externally without cover removal. This is
accomplished by pushing in and turning the external reset knob at
the rear of the valve (see Fig. 2). This feature provides a signicant
system-restoration time advantage.
The Reliable Single Interlock Preaction System trim set (see Fig.
2) provides all of the necessary equipment for connections to the
valve’s pushrod chamber inlet and outlet ports, the main drain,
alarm devices, air supply, water supply, and required pressure
gauges. This valve is provided fully assembled with trim.
System Operation
To fully operate a Reliable Single Interlock Preaction System, two
independent events must coexist before water is discharged. One
electrical detector (two detectors in a cross-zoned system) must
activate and a sprinkler must open. Operation of the detection
system will cause the valve to open, but no water will discharge
since the sprinklers will not have opened. Opening of a sprinkler in
the absence of a detection signal will result in loss of air or nitrogen
pressure and activation of a low pressure alarm.
When set correctly for service, the Model EX Valve is hydraulically
established to withhold the supply water from the sprinkler system
piping. The Reliable Model EX Valve is shown in both closed and
open positions in Fig.2. In the closed position, the supply pressure
acts on the underside of the clapper and also on the push rod
through the push rod chamber’s inlet restriction. The resultant force
due to the supply pressure acting on the push rod is multiplied by
the mechanical advantage of the lever and is more than sufcient to
hold the clapper closed against normal supply pressure surges.
When a re is detected, the energized solenoid valves vent the
air from the pneumatic actuator, which in turn vents the push rod
chamber to atmosphere through the chamber’s outlet. Since
the pressure cannot be replenished through the inlet restriction
as rapidly as it is vented, the pushrod chamber pressure falls
instantaneously. When the pushrod chamber pressure approaches
approximately one-third of the supply pressure, the upward force
of the supply pressure acting beneath the clapper overcomes the
lever-applied force thereby opening the clapper.
Once the clapper has opened, the lever acts as a latch, preventing
the clapper from returning to the closed position. Water from the
supply flows through the EX Valve into the system piping. Water also
flows through the dry pipe alarm outlet to the alarm devices.
After the system is shut down and drained, the Model EX valve can
be reset by pushing in and turning the reset knob at the rear of the
valve (see Fig.2). The external reset feature of the Model EX Valve
provides a means for simple, economical system testing, which is
one essential facet of a good maintenance program.
The external reset feature does not, however, eliminate another
important facet of good maintenance, namely, periodic cleaning and
inspection of the internal valve parts. In the event that water builds
up inside the valve due to condensate from the air supply system
or water left inside from valve system testing, a drain is available
for venting. After closing the main supply valve, a small valve over
the drain cup can be opened slightly until the water inside the valve
body and the main pipe column has drained. See the section titled
“Draining Excess/Condensate Water From System” in this bulletin for
the detailed procedure.
The Model B Manual Emergency Station is also included in the trim
set. It consists of an aluminum nameplate mechanically attached to
a ball valve. The valve handle in its OFF position is guarded against
accidental turning to the ON position (and system discharge) by a
nylon cable tie provided with each trim kit. The cable tie is inserted,
after the system has been restored for operation. The nylon cable
tie is designed to allow, in case of an emergency, forceful turning of
the valve handle to the ON position. As an alternative to the Model B
Hydraulic Manual Emergency Station, the Model A Hydraulic Manual
Emergency Pull Box (see Reliable Bulletin 506) is also available and
can be provided as an option.
Whenever ambient temperature conditions are high, the water
temperature in the Model EX Valve’s pushrod chamber could
possibly increase, thereby increasing the pressure in the chamber to
values exceeding the rated pressure of the system. In an installation
where standard temperatures are exceeded, a pressure relief kit may
be needed. Pressure relief kit, P/N 6503050001, can be installed
into the pushrod chamber’s releasing line to limit the pressure to 175
psi (12,1 bar).
Bulletin 739
January 2021
Page 3 of 9
www.reliablesprinkler.com
Model EX Type A Section and Rear Views
Figure 2
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