Monitoring Systems - Fisher EZL Instruction Manual

January 2008
Type EZL with Type 61L Pilot
Type EZL
INLET
PRESSURE
P590 SERIES PILOT
SUPPLY FILTER
TYPE 61L PILOT
E0959
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
INLET PRESSURE
ATMOSPHERIC PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
ATMOSPHERIC PRESSURE
Figure 3. Type EZL with Type 61L Pilot and Type P590 Pilot Supply Filter Operational Schematic
the aid of a pressure gauge to monitor downstream
pressure. The shutoff valve downstream of the
regulator must not be completely closed; it is necessary
that a small quantity of gas flows downstream to
allow the outlet side to vent, when it is necessary to
lower the pressure.

Monitoring Systems

Monitoring regulation is overpressure protection by
containment, therefore, there is no relief valve to vent
to the atmosphere. When the working regulator fails
to control the pressure, a monitor regulator installed
in series, which has been sensing the downstream
and control pressure, goes into operation to maintain
the downstream pressure at a slightly higher than
normal pressure. During an overpressure situation,
monitoring keeps the customer on line. Also, testing is
relatively easy and safe. To perform a periodic test on
a monitoring 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.
4
SENSE
PRESSURE
LOADING
PRESSURE
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
ATMOSPHERIC PRESSURE
TYPE EZL MAIN VALVE
Wide-Open Monitoring Systems (Figure 4)
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 pressure.
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.
Type EZL