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 of output 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 of pumps, 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 of this paper is the benefits of synchronous, closed transition hand-off between VFD's and utility powered devices in multi-motor applications. Using off-the shelf, 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.