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7.7 Tank Sizing
For constant pressure systems, a pre-charged pressure tank should be used. The tank should be at
least 20% of the pump’s rated flowrate in Gallons Per Minute (GPM). For instance, a pump rated 10
GPM requires at least a 2-gallon tank.
7.8 Troubleshooting Constant Pressure Systems
A variety of conditions in a plumbing system can lead to less than optimum performance of constant
pressure control while using the factory default settings. The default settings are designed to operate a
range of plumbing systems, but there can be many variables in a plumbing system that requires
adjustment of the constant pressure parameters.
In order for the drive to enter sleep mode while operating in constant pressure mode, three conditions
must be met:
1. The pressure in the system must be at the pressure control point set by the parameter psi
SETPOINT.
2. The frequency declines to the shut off frequency (defined as MIN FREQUENCY plus
SHUTOFF FREQUENCY).
3. The time expired since the pump started after the last OFF cycle must be greater than
parameter T1ON or T2ON
When these conditions have been met, the drive will go to sleep. The duration of which the drive is
asleep depends on the rate at which the system bleeds down and the width of the dead band. When
setting and testing a constant pressure system, try to operate as close as possible to the normal
operating conditions. Low flow in a high capacity system (and vice versa) usually requires some
adjusting of the parameters.
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