19
SYSTEM SAFETIES
Overview
The program in the PLC protects the system
by shutting down in either of the “Auto” or
“Manual” Modes of operation if it detects any
of the following problems:
Alarm or Fault
Automatic Restart?
Low Discharge
Pressure
No Automatic Restart
High Discharge
Pressure
Automatic Restart
Low Inlet Pressure
(Optional)
Automatic Restart
Loss of Prime
(Optional)
Automatic Restart
Low Level (Optional)
Automatic Restart
Station Phase
Pressure (Optional)
No Automatic Restart
Individual Pump
Faults
No Automatic Restart
VFD Fault
Automatic Restart
Table 1:
Automatic Restart After Alarm
or Fault
Automatic Mode of Operation
"High Discharge Pressure," “Station Phase
Failure," "Low Inlet Pressure," "Low Level,"
"Loss of Prime," and "VFD Fault" allow the
system to restart automatically when the fault
clears in the automatic mode of operation. The
PLC allows three (3) automatic restarts (which
can be caused by any combination of these
faults) in a one-hour period. At the fourth
occurrence in a one-hour period, the station
shuts down (hard fault). "Low Discharge
Pressure" and "Individual Pump Faults," do
not allow the system to restart automatically
when the fault clears. These faults must be
cleared and manually reset before station
operation can resume. Individual pump faults
require turning the pertinent individual pump
switch to the OFF position, and then back ON
(called, re-arming). In some instances, an
individual pump can trip an alarm without
shutting down the entire system, provided
another pump is available to operate.
Manual Mode of Operation
All faults are cleared by pressing the Reset
button, or by re-arming individual pump faults.
Low Discharge Pressure
The pressure transducer located in your
station discharge line communicates the
downstream pressure to the PLC. The PLC
monitors downstream pressure to determine if
the pressure is below the allowable range.
The standard PLC program defines low-
discharge pressure as being 25 PSI below
setpoint pressure. There is a time delay of 300
seconds (five minutes) before the station
faults that is designed to give the system time
to build pressure beyond this point. The
values might vary on your station.
Based on the values above, if the discharge
pressure remains 25 PSI below the setpoint
for longer than five minutes, all pumps are
shut down. The red station fault light on the
control panel door comes on, and the display
indicates that a "Low Discharge Pressure
fault" has occurred.
This fault does not automatically reset. To
clear the fault, press the Reset button. The
station runs for another five minutes before
determining whether the low discharge
pressure condition still exists.
NOTE:
If you are attempting to run in
automatic
line
fill
mode,
place
the
Override/Active switch in OVERRIDE. Return
switch to the ACTIVE position once the
pressure is high enough to do so.
If the pump station is simply unable to keep up
with the demand, shut the station down, and
determine the nature of the problem. Consult
the Troubleshooting section of this manual for
assistance.
High Discharge Pressure
As with the "Low Discharge Pressure" fault,
the PLC monitors downstream pressure to
determine if the pressure is out of range, or
above the allowable limit.
The standard PLC program defines high-
discharge pressure as being 15 PSI above
setpoint pressure. There is a time delay of
60 seconds, or one minute, before the station
faults that is designed to give the system time
to adjust the pressure to below this point.
These values might vary on your station.
Based on the values above, if the discharge
pressure remains 15 PSI above the setpoint
for longer than one minute, the station shuts
