September 2010 Electrical Apparatus

September 2010 Electrical Apparatus

This is a summary of the Electrical Apparatus September 2010 featured technical article,  by Richard L. Nailen, P.E.

For some time, motor rewinds–and electrical repairs generally–have been a decreasing share of the market available to the typical apparatus service center. Responsible for much of that trend has been the growing emphasis on replacement of failed industrial motors by newer, more efficient designs, often subsidized by some governmental agency or public utility.

Service industry leaders have therefore emphasized the advantage to repair shops in becoming proficient in machining, welding, and other mechanical repairs to non-electrical equipment. A source of such business that is readily available to many shops is the municipal or utility water and wastewater treatment facility. Every community is served by such an agency, and motor-driven centrifugal pumps are essential to their operation. Pump reliability is important to community welfare. Downtime must be minimized, and repair facilities must be close at hand.

Also, utilities in particular tend to think of the motor and pump as forming a single unit. Formerly known primarily as the provider of motor repairs, the apparatus service center is in a good position to take over the associated pump repair as well.

Pump life tends to be much shorter than for a motor. Bearings and seals are the most common failure causes. Vibration, unbalance, and misalignment (with which a motor repair shop is already familiar) are frequent pump troubles. An important contributor to pump unbalance is cavitation–the erosion of the pump impeller caused by the high impact of bubbles in the pumped fluid, as they violently collapse again metal surfaces under abrupt pressure changes. Rebuilding of impeller contours, then careful rebalancing, is an essential repair. Whereas electrical repair or redesign can only maintain original motor efficiency, or add a percentage point or two, pump efficiency is initially much lower and can be raised as much as 30 to 50 points by careful repair.

Shop machining capability may need enhancement. And repair welding of cracked pump casings–normally cast iron–is another important shop skill. But the investment can be well worth while.

To order a back issue with the full article, “Pump repair  – a natural for the service center,” call 312-321-9440 or visit our online webstore.

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