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Pre-Charge Mode
When filling a large plumbing system with water, it may be desirable to fill at a slow pump speed so that when
the system reaches the full point, water hammer does not cause damage such as sprinkler head blow-off or
burst pipes. To achieve this, DXL and LHX drives are equipped with a pre-charge feature.
Analog constant pressure systems can implement a low-flow pre-charge of the system plumbing before the
pump is allowed to come to full speed. This feature is disabled if the 1.4.10 PRECHARGE TIME parameter is
set to zero. For both types of CP systems, the frequency of the pump will not exceed the value set by the 1.4.9
PRECHARGE FREQUENCY parameter during the pre-charge interval.
An analog CP system has the same features with the added option that the pre-charge interval will terminate
when the system pressure exceeds the setting of the 1.4.11 PRECHARGE PSI parameter. In this case, the
1.4.11 PRECHARGE PSI must be lower than the 1.4.1 ANALOG SETPOINT 1.
In both CP systems the pre-charge interval occurs whenever the drive is switched from OFF to AUTO or
MANUAL → RUN.
Pre-charge Mode Setup:
1. Navigate through the keypad menu to 1.4.9 PRECHARGE FREQUENCY Enter the Pre-charge
frequency
2. Navigate through the keypad menu to 1.4.10 PRECHARGE TIME. Enter the Pre-charge time in
seconds
3. For analog CP systems only, navigate through the keypad menu to 1.4.11 PRECHARGE PSI.
Enter the pre-charge pressure in psi. This value must be lower than the 1.4.1 ANALOG SETPOINT
1
4. Set the keypad to AUTO mode to operate the system.
6.4 Lead/Lag Pump Control
When any analog constant pressure system configuration is selected, the Lead/Lag menu is available. See
Table 21 for lead/lag control options. Up to four additional pumps can be controlled through programmable
relays on the main control printed circuit board. When the parameter 1.5.1 NUMBER LAG PUMPS is greater
than 0, all four relays will convert to control of lead/lag constant pressure.
CAUTION: Activation of lead/lag control overrides the function of all programmable relays. Any function of
these relays set up through the Interface Parameters (Table 21) will be disabled.
Lead/lag control in pumping systems is a common practice to maintain pressure with highly variable flow. The
system is typically configured with a master pump controlled by a VFD operating in constant pressure mode,
and with auxiliary pumps that are controlled by the drive. The auxiliary pumps typically operate across-the-
line at 60 Hz. They may be equipped with a soft starter to mitigate inrush currents.
If the master pump cannot maintain system pressure it will call for an auxiliary pump by closing a relay on the
Control Terminals. DXL and LHX Series drives can control up to four auxiliary pumps. There are features to
reduce oscillations and ensure smooth staging and destaging pumps.
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