FL Series
3
keeps the customer on line. Also, testing is relatively
easy and safe. To perform a periodic test on a monitor-
ing regulator, increase the outlet set pressure of the
working regulator and watch the outlet pressure to
determine if the monitoring regulator takes over at the
appropriate outlet pressure.
Wide-Open Monitoring Systems (figure 3)
There are two types of wide-open monitoring systems:
upstream and downstream. The difference between
upstream and downstream monitoring is that the
functions of the regulators are reversed. Systems can
be changed from upstream to downstream monitoring,
and vice-versa, by simply reversing the setpoints of the
two regulators. The decision to use either an upstream
or downstream monitoring system is largely a matter of
personal preference or company policy.
In normal operation of a wide-open configuration, the
working regulator controls the system’s outlet pres-
sure. With a higher outlet pressure setting, the monitor
regulator senses a pressure lower than its setpoint and
tries to increase outlet pressure by going wide-open. If
the working regulator fails, the monitoring regulator
assumes control and holds the outlet pressure at its
outlet pressure setting.
Figure 2. Type FL Operational Schematic
E0827
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
PILOT SUPPLY PRESSURE
ATMOSPHERIC PRESSURE
Working Monitoring Regulators (figure 3)
In a working monitoring system, the upstream regulator
requires two pilots and it is always the monitoring
regulator. The additional pilot permits the monitoring
regulator to act as a series regulator to control an
intermediate pressure during normal operation. In this
way, both units are always operating and can be easily
checked for proper operation.
In normal operation, the working regulator controls the
outlet pressure of the system. The monitoring
regulator’s working pilot controls the intermediate
pressure and the monitoring pilot senses the system’s
outlet pressure. If the working regulator fails, the
monitoring pilot will sense the increase in outlet
pressure and take control.
Note
The working regulator must be rated for
the maximum allowable operating
pressure of the system because this will
be its inlet pressure if the monitoring
regulator fails. Also, the outlet pressure
rating of the monitoring pilot, and any
other components that are exposed to
