Bret McCormick
Stewart’s Electric Motor Works, Inc. 
 
The following is an example of how Stewart’s Electric Motor Works was able to provide valuable new service to an existing customer. I hope you can benefit from this case study.

One of our municipal customers was experiencing diminished flow rates and severe leaking from an ITT 600 hp, 1200 rpm split case pump. The pump was brought to our facility for evaluation.

We found its overall condi­tion to be in serious disrepair. The rust and scale from years of service had built up around the packing; the inside of the pump had rust blooms through­out. The shaft sleeves were worn out and the sealing glands were bent. One of the bearing journals was worn and the other had broken.

We also found that the impeller had many holes from wear, electrolysis and cavitation. While researching our customer’s options, we found that to replace the pump with a new model the price would have been well above $250,000 (U.S.). We advised the cus­tomer that the best, most cost-effective option would be to repair the old pump using new components, materials and features that would make it better than new at a more reasonable cost. And, we could do it for significantly less than the cost of buying the new one.  We received the go-ahead to make the repairs.

A challenging project
We had to formulate a plan. We had successfully rebuilt many split case design pumps, but this one would prove to be our most challenging pump project to date.  
Since we knew that we would be coating the pump’s interior, our first step was to place the pump halves into our burnout oven to remove all the old paint and begin to attack the extensive rust and scale. After the heat cleaning cycle, the castings were sandblasted inside and out. The one-two punch of heat and sand made the parts look like new. 

The exterior of the pump was primed and the task of coating the interior got underway. We used En­econ’s Chemclad® XC, an NSF/ANSI 61 certified product. (Other high-quality alternative products are available.)  The process included using a base coating, then an overcoat. In all, three coats of epoxy were applied to the casting interior. See Figure 1. When the new impeller arrived, it was then bead blasted to profile all the non-mating surfaces so the epoxies would adhere. After bead blasting, it was dynami­cally balanced. Then the impeller also received a primer coating and then two more of the overcoat.

We set out to find a way to retrofit the old graphite packing system with split mechanical seals.  Because the shaft sealing sleeves needed to be replaced, we began the small modifi­cations of two new sleeves that would best match the split mechanical seals we would be utilizing. A dye-penetrant was applied to determine if the old shaft had any issues. We then fabri­cated a plate for each end out of steel after finding that while brass was easy to work with, it was not rigid enough to support the stationary part of the seal’s seat.

Machining the body  
We then began the process of machining the body of the pump. It was necessary to over-bore the areas where the packing formerly was lo­cated, along with repairing the bear­ing journals. Since accuracy was most important in this case, both halves were mated, gaskets installed and then line-bored. 

After machining, the process of the assembly began. The impeller, shaft, and shaft sleeve assembly were then placed in the bottom half of the pump. The new wear rings were put in along with the seal seat stationary plates. Then the self-aligning bearings were installed on the shaft and adjusted to support the impeller. See Figure 2. Finally the split seals were in­stalled and adjusted.   We worked very closely with the Chesterton Company throughout the process of specifying and installing the new seals.

We then over-coated the exterior of the pump with Amerlock® 400, a 2-part high-solids epoxy paint system, designed for industrial use. (Other high-quality alternative products are available.) See Figure 3

The customer reported increased flow rates from 9000 gallons per minute (gpm) to close to 11500 gpm, reflecting a 22% improvement. From a realistic point of view since the impel­ler was worn so badly, replacing the impeller and the application of the coatings likely increased the overall efficiency of the pump between 3 - 5%.

With the experience gained from this project, we got the benefit of continuing to expand our range of services to our current customers and demonstrate our capabilities to new customers.

Categories: Case studies, Pumps

Tags: Pumps Case study

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