Municipal water distribution systems contain thousands of miles of underground pipes to distribute potable water to homes and businesses.
In order to supply water across long distances, and to reach all points within the distribution system, large pumping facilities are used to maintain water system pressure within these pipes.
Water Hammering
But what happens when the pressure varies suddenly? Rapid changes in the water flow rate result in high-pressure build-up and high surge forces. This condition is called “water hammering” and it occurs in underground pipes when a pump accelerates or decelerates to full speed or zero speed too quickly.
“Water hammering” can burst pipes which can severely disrupt municipal water distribution systems until costly repairs are undertaken to fix the breaks, but this solution does not address further problems.
A Recommended Solution
Using a VFD to slowly vary the electrical system frequency, the motor speed can be gradually increased or decreased
To mitigate “water hammering”, users should consider a Variable Frequency Drive (VFD), electrical equipment that can vary the frequency of an AC power source.
Since the speed of an AC motor is directly proportional to the frequency of the electrical supply, controlling “water hammering” is a function of the quality of the electrical system.
Using a VFD to slowly vary the electrical system frequency, the motor speed can be gradually increased or decreased to establish a suitable pump speed. With this operating philosophy, users can avoid the sudden changes in the water flow rate that cause “water hammering.”
The Best Solution
Users can further mitigate “water hammering” with a technology known as “flying restart”. Instead of an abrupt “off” like slamming the brakes in a car, a “flying restart” is like stopping the car by gradually easing pressure off the accelerator.
The concept is that when electricity is restored following an outage, the pump will come back on without an abrupt speed variation, thus avoiding the hammering of the water supply. To further improve reliability in the water distribution system, the concept of “flying restart” can be implemented using a specialized Variable Frequency Drive (VFD).
flying restart technology
A specialized VFD, using “flying restart” technology will allow the motor to restart
During a momentary utility power outage, a typical electrical motor would immediately shut down due to the power loss, and even when power is restored, the pump would continue its sudden deceleration to cause water hammering.
However, a specialized VFD, using “flying restart” technology will allow the motor to restart even while the motor is already coasting down, which prevents the need to wait for the motor to reach a complete stop.
restoring normal operations
By catching a motor/pump on the fly using “flying restart”, the motor speed can be quickly matched and synchronized by the specialized VFD.
Using “flying restart” technology, the effect of water hammering is again greatly reduced since the pump can be gradually restored to normal operation as soon as electricity is restored.
