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Figure 14. Working Monitoring System Operational Schematic with Two EZH (Spring-to-Close) for DN 25, 50 and 80
Type SA/2
V
R
M
Inlet pressure (P
)
INLET PRESSURE (Pu)
u
Motorization pressure (P
MOTORIZATION PRESSURE (Pm)
Pilot feeding pressure (P
PILOT FEEDING PRESSURE (Pup)
Outlet pressure (P
)
OUTLET PRESSURE (Pd)
d
Atmospheric pressure (P
ATMOSPHERIC PRESSURE (Pb)
Working Monitor System with
Type PRX Pilot (Figure 14)
In a working monitoring system, the upstream regulator
requires two pilots and it is always the monitoring regulator.
The additional pilot Type PRX/125 or PRX/125-AP 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 Type PRX/120 or PRX/120- AP controls the
intermediate pressure and the monitor pilot Type PRX/125
or PRX/125-AP senses the system's outlet pressure. If the
working regulator fails, the monitoring pilot Type PRX/125
or PRX/125-AP will sense the increase in outlet pressure
and take control.
Type
Type
PRX/120
PRX/125
S
B
L
A
R1
Type EZH
)
m
)
up
Type PRX:
S - Bleed port
)
B - Supply port
b
Types EZH and EZHSO
R2
S
V
R
B
L
Type SA/2:
V - Sensing
L - Motorization port
R - Pilot
A - Sensing port
M - Inlet
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 Type PRX/125 or
PRX/125-AP and any other components that
are exposed to the intermediate pressure
must be rated for full inlet pressure.
Type SA/2
M
Type EZH
CAUTION
!
Type PRX/120
S
B
L
A
R100
13
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