3.2 REGULATOR - ACTIVE / MONITOR SYSTEM
In the active / monitor system, the regulator working principle is similar then previously explained.
The upstream regulator (monitor) keeps in the open position, because the pilot sensing line monitors the active
pressure regulator set point and, as its set point is lightly higher, the pilot keeps opened. The reason that this pilot stays
opened is due of pressure under its diaphragm that added to the obturator spring that are lower than the regulating spring
force that moves this obturator set downward opening the pilot.
With this, the pressure in the diaphragm upper chamber in the monitor regulator keeps lightly lower than the inlet
pressure allowing the valve stays in the open position during normal process service conditions.
In case of active regulator fail that results in increase in outlet pressure, the pilot of monitor regulator start closing up to
achieve the set point of this pilot, and then the monitor regulator can assume the control of pressure reduction in the
system. From this moment, the working principle of this valve is similar then the active regulator.
The configuration of assemblage active / monitor is highly utilized in the gas distribution and transmission. This
configuration is normally adopted when the difference between the inlet and outlet pressure is over than 16 bar and the
strength pressure test in the pipe and other components upstream the regulator is inferior than the inlet pressure as
specified, for example in the standard DIN EN 12186, in this case the objective of use of monitor regulator is to increase
the system safety level.
However, is important to remember that this is a recommendation of DIN EN 12186 and that there are other standards
that specifies different conditions of use of active / monitor system.
The active / monitor system consists of utilization of two pressure regulators in series being one of them called active
that will be in operation (regulating the pressure) under normal process service conditions and one monitor regulator that
should stay totally open under normal process service conditions, and will assume the pressure regulating in case of active
regulator fail.
To Next Page
