Xylem 19 001 200 R2 SILENT STORM VFD Pumping System - Manual (Page 19)

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NOTE: When done, turn OFF all pump
switches and place system control switch in
OFF. Return Override/Active switch to
ACTIVE.
VFD Bypass Operation, Auto mode
Overview
VFD Bypass mode is an EMERGENCY ONLY
mode used when the VFD is inoperative.
Monitor station operation closely when in
bypass mode due to limited pressure control
available. Your station must be equipped with
a PRV (Pressure Reducing Valve) in order to
run VFD Bypass Mode automatically. This
valve now assumes the pressure regulating
function that was performed by the VFD in
normal operation. Ensure that the PRV is
adjusted to maintain your downstream
pressure at no more than 12 PSI above
setpoint pressure. Verify that the PRV is
operating correctly before leaving the station
unattended. Check station regularly to ensure
continued proper operation. If your station is
not equipped with a PRV, do not operate in
automatic VFD bypass mode.
WARNING: VFD Bypass Switch Hazard
This mode of operation should be used as a last
resort if there is no DSR, or it is not functioning
correctly. Constant operator attendance is
recommended when this mode is used. The water
demand must be calculated to match the
individual pump output as closely as possible.
Failure to do so will cause a serious over-pressure
condition.
Failure to follow these instructions could result in
serious personal injury, death, or property
damage.
VFD Bypass mode is selected by the VFD /
Bypass switch. The system control switch
MUST be turned to the OFF position before
selecting VFD bypass mode. Operation is
similar to normal automatic operation but the
start / stop sequences differ greatly. The
registers below regulate this.
NOTE: These are generic values and might
differ from your station.
Pressure below setpoint to start
Combo 1 5 PSI
Delay time to start Combo 1 0 SEC
Pressure above setpoint to stop
Combo 1 5 PSI
Delay time to stop Combo 1 5 SEC
Pressure below setpoint to start
Combo 2 12 PSI
Delay time to start Combo 2 3 SEC
Pressure above setpoint to stop
Combo 2 1 PSI
Delay time to stop Combo 2 60 SEC
Pressure below setpoint to start
Combo 3 15 PSI
Delay time to start Combo 3 10 SEC
Pressure above setpoint to stop
Combo 3 1 PSI
Delay time to stop Combo 3 30 SEC
Flow setpoint to stop Combo 1 0 GPM
Flow setpoint to stop Combo 2 20 GPM
Flow setpoint to stop Combo 3 80% *
Flow setpoint to stop Combo 4 80% **
80% of the previous combo’s maximum
output. * If one main pump puts out 500 gpm,
you would enter 400 gpm here. ** If two main
pumps put out 1000 gpm, you would enter 800
gpm here.
Other significant differences between VFD
Bypass and Automatic VFD Operation are as
follows:
1. The overpressure accumulator is not used
in VFD bypass mode.
2. Flow will dominate stopping main pumps
due to low Combo stop pressure settings.
The PM pump will continue to operate
similarly to VFD mode.
3. VFD Fault and Maximum RPM signals are
ignored.
4. Pump starts are caused by pressure drop
as in VFD mode, but due to operational
differences, the settings are modified from
those used in VFD mode.
Sequence of Operation (performed in
order)
System control switch: OFF
All Individual Pump switches: ON