Outcome Reversed

April 2, 2018
Florida Water Utility incorporates detection system to halt unwanted reverse rotation in pump

Electro-Sensors, Inc.

6111 Blue Circle Drive * Minnetonka, MN 55343

Phone 952/930-0100

www.electro-sensors.com

George Osterberg of the Palm Beach County (Fla.) Water Utility related a situation that occurred in his facility recently. It involved unwanted reverse rotation of a high service pump.

"Reverse rotation occurs because of a backpressure condition that can develop in the piping system after the pump is shut off," said Osterberg. "Seepage back into the pump is always a possibility. At our water utility in Palm Beach, reverse rotation occurred unexpectedly in one of our pumps.

"The problem began to develop when we experienced a power failure from our primary electrical supplier, Florida Power and Light. Normally, our pumps are protected from backpressure with an electrically actuated hydraulic valve system. Because of the power failure, this valve did not close completely after the pump was shut off and backpressure seepage caused the pump to begin rotating in reverse.

"Our emergency generator kicked in and continued to close the hydraulic valve" Osterberg continued. "At the same time, water demand increased and the pump was called back into service. When the 800-hp motor that drives the pump was started, it delivered full torque to the pump shaft that was still turning in reverse. This caused the 4-in. diameter pump shaft to snap rendering the pump out of commission. The time and expense of repairing the pump was considerable."

Answer found

The solution involved developing or acquiring a low-cost system to detect shaft reversal that would safeguard pumps from potentially damaging reverse rotation. This system needed to be simple to install, operate automatically and, above all, be reliable.

After an extensive Internet search, a system made by Electro-Sensors, Inc., was found.

The company offered the ideal shaft reversal detection system, the UDS1000. This system uses a non-contact, bi-directional rotation sensor combined with a signal generating magnetic collar installed on the pump shaft. It continuously monitors incoming pulses from the rotation sensor and magnetic collar. The unique circuitry of this product employs a failsafe switch output--an isolated relay--that is electrically interlocked directly with the motor starter circuit for the pump.

If the slightest reverse rotation of the pump shaft is detected, it disables the pump starting circuit, thus preventing start-up during reverse rotation When the pump stops turning in reverse, the system automatically resets itself to allow a normal, safe start-up. Because the UDS1000 is failsafe, a power failure, as in this case, would de-energize the relay. This means the starting circuit to the pump motor would still be disabled. Upon restoration of power, the UDS1000 relay resets but would instantaneously switch out again if it detected a shaft reversal, thus preventing the pump motor from starting during a reversal condition and eliminating the problem.

All components of the detection system are corrosion resistant and designed for water utility usage. The Palm Beach County Water Utility discovered reliable protection for their critical high service pump after installing the UDS1000 Shaft Reversal Detector System.

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