Data Sheet

Bulletin 71.2:310A
4
throttling sleeve toward the stationary valve plug to
decrease the gas ow to the downstream system.
The top diaphragm in the pilot acts as a sealing
member for the loading chamber and as a balancing
member to the bottom diaphragm. The two
diaphragms are connected by a yoke. Pressure
change to the center chamber has little effect on the
positioning of the valve disk.
Monitor Systems
Wide-Open Monitors (Figure 3)
Monitoring regulators serve as overpressure protection
devices to limit system pressure in the event of failure
of working regulators feeding the system. The control
line of a wide-open monitoring regulator may be
connected downstream of the working regulator, so
that during normal operation the wide-open monitoring
regulator is standing wide open with the pressure
reduction being taken across the working regulator.
Only in case of working regulator failure does the
wide-open monitoring regulator operate.
Working Monitors (Figures 4 and 5)
The Type 310A-32A-32A working monitor regulator
differs from wide-open monitors in that it has working
monitor capability. This means that it normally
reduces pressure and throttles while the second-stage
regulator is in operation. Should the second-stage
working regulator fail open, the Type 310A-32A-32A
will take over the entire pressure reduction function.
The working monitor pilots are adaptations of two
Type 32A pilots with special internal parts, due to
the pressure conditions in this piloting system. A
spacer blocks open the differential regulator portion
Figure 3. Typical Wide-Open Monitor Figure 4. Typical Working Monitor
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of the Type 32A monitoring pilot. A plug in both the
working and monitoring pilots makes the internal
bleed nonfunctional. A restriction placed in the
external tubing between the diaphragm loading
pressure and the intermediate pressure acts as a
downstream bleed.
If the second-stage working regulator fails to open,
the distribution pressure increases to the setting of
the Type 32A monitoring pilot (slightly higher than
the original distribution pressure) and is controlled
at that level by the Type 310A-32A-32A. Thus,
downstream equipment is protected against a major
overpressure condition without disrupting service or
venting gas to atmosphere.
In the working pilot, the inlet pressure is reduced
to a pre-determined pilot supply pressure, which is
further reduced to loading pressure for the Type 310A
diaphragm. The loading pressure is piped through
the portion of the monitoring pilot blocked open by the
spacer and, as long as distribution pressure is below
the setting of the monitoring pilot, passes through the
relay orifice of the monitoring pilot to the diaphragm
case of the Type 310A body.
Distribution pressure is piped back to the monitoring
pilot. As long as the distribution pressure is less than
the monitoring pilot setting, the working pilot controls
the Type 310A to maintain intermediate pressure. If
the distribution pressure increases to the monitoring
pilot setting, the monitoring pilot relay orifice starts
to throttle the loading pressure to the Type 310A
diaphragm. This allows the Type 310A main spring
to move the throttling sleeve closer to the seat and
control distribution pressure at the monitoring pilot set
point. Therefore, failure of the second-stage working
regulator is controlled with only a slight increase in
distribution pressure, with the Type 310A-32A-32A
accomplishing the entire pressure reduction function.