Xylem IM167 R8 Aquavar CPC (Centrifugal Pump Control) - Manual (Page 87)

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MultiPump – Constant Pressure Control
Overview
The Aquavar CPC has the ability to connect and control up to four centrifugal pumps, to
form a Multi-Pump, lead-lag and alternating pumping system. This will allow the operator to
maintain a constant pressure through a larger system flow range, and provides equal wear for
the pumps and motors. The Aquavar units will be hard wired together via the RS485 terminals
(29,30,31), and provide communication to maintain a constant pressure to the system. Once
the lead pump cannot maintain a certain pressure and allows a slight pressure drop, the next
(lag) pump will turn on and vary the speed according to the flow demand. This sequencing
can be programmed according to the specific system requirements, and is field adjustable. If
a pump or controller fails, the next pump will automatically turn on in its place. Each Aquavar
controlled pump will provide a fully functional lead/lag and automatic alternation system, with
automatic back up control when required.
System Curve - Friction Compensation
It is possible to program the Aquavar to maintain a constant pressure, and compensate for
increasing friction loss according to a system curve. As the flow rate increases in the system,
the friction loss will increase as well. The Aquavar can compensate for this friction loss with
the simple adjustment of the parameter 2202 “VALUE INCREASE”. When each Aquavar unit
enables the pump, it will increase the system pressure by the programmed amount. This
pressure is additive with each additional pump. Therefore, if you set this parameter for 3 psi,
and you initial constant pressure is 50 psi, and you have 4 pumps total: (50 psi + 3 psi + 3
psi + 3 psi) = 59 psi when all 4 pumps are operating at full speed. This final system pressure
should be enough to overcome your calculated head and friction loss, and to provide constant
pressure at the end of the pipe run. NOTE: This program function is not intended for
substitution of proper pipe layout and sizing according to Hydraulic Institute Standards.
This feature may not work for excessive friction losses!
Pump Sequencing
The Aquavar CPC has the ability to operate in a multiple pump with lead and lag pumps.
Each Aquavar will be given an address then operate as Pump 1, Pump 2, Pump 3 or Pump 4.
When Pump 1 cannot maintain the required system pressure and the speed reaches 60 Hz,
then that will trigger the lag pump to come on and help maintain the set pressure. In order
for the lag pump to turn on, the lead pump must be at full speed (Maximum Frequency)
and programmed system pressure drop must be met (VALUE DECREASE). Each Aquavar
controlled pump will vary its speed according to the demand on the entire system. In a
Duplex System, you could have Pump 1 running at full speed 60 Hz, and Pump 2 running at 50
Hz in order to maintain the system pressure at the flow demand. Each pump will operate in a
sequential mode, when called.
PROGRAMMING