Xylem IM255 AQUAVAR Intelligent Pump Controller - Manual (Page 85)

Prime Limit [22-39] based on the affinity laws to determine the actual power limit for the
No Water/Loss of Prime function. Since pump power consumption changes with the cube
of speed and the No Water/Loss of Prime Limit is entered as 85% of maximum speed, the
controller scales the power entered in No Water/Loss of Prime Limit [22-39] by (1/85%)
3 or
1.628 to determine the actual power limit used for the No Water/Loss of Prime function.
When the pump is running at full speed and the actual power consumed by the pump is
less than or equal to this value for a specified amount of time, the No Water/Loss of Prime
alarm is issued. It is recommended to set this value by performing the No-Flow Power
Calibration Setup.
NOTE: If the Autoset function is used to configure the controller this value is set to 75% of
the service factor HP multiplied by the 85% speed ratio cubed (or (85%)
3 = 0.614) of the
pump/motor combination. For example, for a 10HP pump/motor with a pump/motor
service factor of 1.15 (the pump utilizes 100% of the service factor of the motor), the
Autoset function sets the No Water/Loss of Prime Limit [22-39] to 5.29HP.
The Power Correction Factor [22-31] can be used to modify the internal scaling of the No
Water/Loss of Prime Limit [22-39] in cases where nuisance tripping results or where a No
Water/Loss of Prime condition is not detected. If nuisance tripping results, the Power
Correction Factor [22-31] can be increased above 100%. Increasing the Power Correction
Factor [22-31] will increase the scaling of the No Water/Loss of Prime Limit [22-39] so that
a No Water/Loss of Prime condition is detected at a higher power. The amount of increase
above 100% is dependent on the loading of the pump. If a No Water/Loss of Prime alarm
is not issued when the pump has lost prime or runs dry the Power Correction Factor
[22-31] can be decreased so that a No Water/Loss of Prime condition is detected at a
lower power. The amount of decrease below 100% is dependent on the loading of the
pump.
The No Water/Loss of Prime Restart function can be set to allow the controller to attempt
to restart the pump after a specified amount of time. In order to enable this function a
jumper wire must be installed between terminals 29 and 32. Refer to the Common
terminal wiring configurations section in this manual for details on control terminal wiring.
The default restart time is 10 minutes. Set this value based on the system requirements.
The No Water/Loss of Prime Protection Delay [22-27] is the time delay between detection
of the No Water/Loss of Prime condition and the action of the No Water/Loss of Prime
Alarm. The No Water/Loss of Prime Protection Delay [22-27] time can be extended to
avoid nuisance tripping. Note that extending the time will allow the pump to run dry or
without prime for the time specified.
NOTE: It is recommended to set the No Water/Loss of Prime Protection Delay [22-27] time
shorter than the Under Pressure Delay Time [22-51]. This ensures a No Water/Loss of
Prime condition will be detected properly before the Under Pressure function is triggered.
Operation
Aquavar ® Intelligent Pump Controller INSTRUCTION MANUAL 83