Xylem 19 001 251 R3 Floboy VFD Pumping System - Manual (Page 21)

17
AUTOMATIC OPERATION
Overview
The primary benefit of Variable Speed Pumping
(VSP) Systems is to ensure surge-free starts and
stops while maintaining a constant down-stream
line pressure with no mechanical pressure-
regulating valve. This minimizes pipeline failures
due to surges and, not incidentally, reduces the
utility bill for the station.
Automatic operation is selected by manual-Auto
control on the HMI. In automatic operation, all
pump activity is determined by the controller. The
position of the individual pump switch lets the
controller know whether or not it is available to
run. In most cases, all pump switches are in the
ON position. When a pump or a motor is removed
from the system, turn the pump switch OFF, and
the controller will not try to run that pump.
The controller brings one pump on at a time in
order to satisfy the start criteria (usually set point
pressure). Some stations are designed to start and
stop the pumps based on remote start signals or
flow. The standard start and stop sequence is as
follows:
Pressure below set point to start
Combo 1 -3 PSI
Delay time to start Combo 1 0 SEC
Pressure above set point to stop
Combo 1 5 PSI
Delay time to stop Combo 1 5 SEC
Pressure below set point to start
Combo 2 -5 PSI
Delay time to start Combo 2 3 SEC
System Charging Mode
If there are no heads open, and the pressure is
within the defined range of operation, pressure
may slowly drop due to system leakage, or other
small demands. A PM pump option is available to
address this issue. Not all stations include a PM
pump. System is configured as follows:
System Mode: AUTO
All Individual Pumps switches: ON
LP Override Setting: Off (Low Discharge Pressure
fault enabled)
NOTE: As downstream pressure drops to more
than 5 PSI below set point, the PM pump starts
up. It runs until the system pressure builds up to 5
PSI above set point, and then shuts off.
Two issues can come into play here. One is cycle
time. This refers to the number of times an hour
that the PM pump starts and stops (one cycle). If
the amount of cycles is excessive, either the
system leaks have to be repaired, or the start/stop
parameters need to be tuned (normally by
dropping the pressure below set point to start or
increasing the pressure above set point to stop).
WARNING: Excessive Run Time Hazard
Excessive stop times, or stop pressure setting
can cause system over-pressurization, pipe
damage, and potentially cause personal injury.
Consult your service technician or the factory if
you are unsure about any settings.
Failure to follow these instructions could result in
serious personal injury or death, or property
damage.
NORMAL OPERATION
Normal Operation occurs when heads are turned
on, or a demand for water exists. System is
configured as follows:
System control switch: AUTO
PM Pump switch: ON
Pump 1 switch: ON
LP Override setting: “N” (Low Discharge
Pressure fault enabled)
When the pressure drops 5 PSI below set point,
the PM pump starts and continues to run until the
pressure is 5 PSI above the set point. When this
pressure is reached, the PM pump turns OFF. If
the pressure continues to drop to 10 PSI below set
point, the VSP starts and the PM pump turns OFF.
This is the operation sequence for Combo 1.
When the VSP starts, the startup ramp in the
program lowers the set point to 2 PSI above the
actual line pressure. The VFD adjusts the speed of
the VSP to maintain the discharge or downstream