54 | P a g e
when the motor is turned off, how long it is off, and also prevent short cycling of the motor at low water
flow rates. More information including default values for these parameters can be found in Table 15,
Constant Pressure Parameters.
DRAWDOWN PSI and BOOST AMOUNT
The primary method of preventing short cycling is to allow a differential between the pressure at which
the pump turns off to enter sleep mode and the pressure at which it restarts. Two parameters,
DRAWDOWN PSI and BOOST AMOUNT, control this differential. BOOST AMOUNT specifies the
increase in pressure above psi SETPOINT just before the pump shuts down to enter sleep mode, while
DRAWDOWN PSI specifies the pressure drop below psi SETPOINT at which the pump restarts. For
example, assume psi SETPOINT = 50, BOOST AMOUNT = 5, and DRAWDOWN PSI = 5. When the
pump is ready to enter sleep mode, the pump will boost to 55 psi, then restart when the pressure falls to
45 psi. These two parameters can be used together or independently to create a dead band in
pressure control.
Both OVERPRESSURE PSI and SHUTOFF FREQUENCY cause the drive to enter sleep mode.
OVERPRESSURE psi is additional system protection. It is a value that is added to the psi SETPOINT.
The default value for OVERPRESSURE psi is 20. For example, if the psi SETPOINT is 50 psi, the
drive will stop the motor if pressure reaches 70 psi.
The parameter SHUTOFF FREQUENCY is used to put the drive in sleep mode when pressure is
controlled and flow is low. Shut off frequency is a value that is added to MIN FREQUENCY. For
example, if minimum frequency is 30 Hz and shut off frequency is 12, the drive will enter sleep mode at
42 Hz. When a value of zero is entered for the parameter SHUTOFF FREQUENCY, sleep mode is
disabled.
CAUTION: When sleep mode is disabled in low flow conditions, the drive will slow down to
minimum frequency and continue to run. Inadequate water flow in this condition may overheat and
damage the pump.
ON/OFF Cycle Timers
The drive records the length of time the motor remained in the OFF cycle and compares that time to the
parameter, TOFF. If the motor-off time during the last OFF cycle was greater than the value of TOFF,
then the minimum motor-on time will be equal to T1ON. If the motor-off time was less than TOFF, the
minimum motor-on time will be equal to T2ON.
In other words, the time of the last OFF cycle determines whether the next ON cycle should be relatively
long or relatively short. The graphic in Figure 31 demonstrates how the system adjusts the motor-on
time in response to motor-off time.
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