The Not-So-Silent Risk of Improper Controls – Water Hammer

Whether large or small pumps, there comes a debate when multiple drive motors are used to
cover a broad range ofoutput flow requirements: use one Variable Frequency Drive (VFD) plus
a number of softstarts, some small and some large pumps with or without VFD’s, one or more
VFD’s on a group ofpumps, and all combinations in between. Equipment rotation and
maintenance, starts per hour, starts per day, minimum flows, maximum demands, etc., all are
considerations and decisions to be made. Many of these combinations invoke unintended
hydraulic consequences. The focus ofthis paper is the benefits of synchronous, closed transition
hand-off between VFD’s and utility powered devices in multi-motor applications. Using off-theshelf,
standard, available equipment that can synchronize drive output with across-the-line loads,
the best of numerous options can be had while reducing power costs, protecting personnel and
equipment, and achieving process control.