Mike Dolt Enterprises
Mike Dolt Enterprises
User: ptonsparky, Location: NE (9.06 miles @5.9 Degrees from Winged Horses)
Asked on: Tuesday, April 5, 2011 at 12:12 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:47 am EDT
Question: Customer with two irrigation wells feeding one Pivot. Neither pump is able to supply the water requirements of the Pivot. Both pumps have VFDs and are located remotely from each other. This is the first year that both will feed the pivot. I feel that unless one pump is made the primary source and allowed to run at full speed both pumps will "search" while trying to maintain 35# of pressure.As one pump increases output the other will drop with the PID loops of both acting against each other.Yes/No or a case of HUA and no need to worry?
Yes, you are correct in your assessment.
Problem
When two pumps with VFDs feed a single irrigation pivot, they can engage in a "searching" or oscillatory behavior, especially if neither pump can independently supply the pivot's water requirements.
Reason
Both pumps have PID (proportional-integral-derivative) control loops. When one pump increases output, its PID loop senses the pressure increase and reduces its output. This triggers the other pump's PID loop to increase its output to maintain pressure. As a result, the two pumps repeatedly cycle between increasing and decreasing output, resulting in an unstable pressure and uneven water distribution.
Solution
To prevent this "searching" behavior, you need to designate one pump as the primary source and make sure it runs at full speed. This pump should be capable of supplying the majority of the pivot's water requirements. The secondary pump should then be set to operate in standby mode or at a reduced speed to supplement the primary pump when needed. This will ensure stable pressure and efficient water delivery.
HUA (Head Up Against):
HUA is not a concern in this scenario, which involves pumping water into a pivot rather than into a different water system. Flag for review