5
Figure 5. MBF-M Series Operational Schematic
OPERATION
The range of position of control member depend from actuator assembly (spring-stem-diaphragm) movements.
The Diaphragm divides the Regulator control head into two chambers. The lower chambers is connected to regulated pressure Pd,
and the other, where the spring regulator is located, is connected to atmospheric pressure.
When the contrasting actions of the spring and outlet pressure coincide, the mobile diaphragm-stem-valve assembly remains motionless,
and outlet pressure matches spring set point.
An increase in capacity demand will cause a decrease in outlet pressure. This means that the spring’s action will prevail over outlet
pressure’s action, and the valve will open until set point pressure is again reached at outlet.
The opposite occurs whenever outlet pressure increases.
Precision perfect balancing of control member is assured under all operating conditions by the inlet pressure which operates in the
counterbalancing chamber.
The monitor or emergency regulator is used as a safety device in gas pressure reduction systems. The purpose of this device is to
protect the system against possible overpressure, while keeping the reduction line in service.
The monitor controls downstream pressure at the same point as the main regulator and is set a little higher than the latter.
Under normal duty, the monitor is fully open as it detects a pressure value lower than its set value. If, due to any regulator fault,
downstream pressure increases, when it exceeds the tolerated level, the monitor comes into operation and adjusts pressure to its
own set value.
For the OS/66 slam-shut controller operation please see the 0048EN-OS66-IM instruction manual.
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