Pump Rebuild Boosts Efficiency & Max Flow

Nearly every business, industry, municipality, school and home has and uses pumps. They pump everything from drinking water and wastewater in cities and towns to heavy aggregate solutions in mines, quarries, power plants, and in oil and gas fields. As common as pumps are, when normally functioning they are often overlooked until they need attention. This usually shows itself in a few ways:

• increasing bearing noise
• sudden increase in vibration
• pumping output dropping 25 to 50 percent, which shows up as an increase on the electric bill

For discussion here, a homeowner takes a walk outside early one Saturday morning and hears his 17-year-old pool pump screaming for attention. Then, after a quick analysis and $150, the homeowner picks up the new motor, swaps it out and the summer fun continues. Now, let’s scale this up to industrial application proportion and to situations many of the engineers, managers and maintenance professionals either have run into or likely will in the future. Situations like this happen in the industrial workplace all the time requiring analysis of the situation, investment in repairs or new equipment and potential for very high downtime costs. The untimely failure of a single piece of equipment like a pump can lead to astronomical costs, and they can add up in a hurry. There are many types of pumps in an array of industries that, at some point or another, require service and maintenance to optimize their functionality. At one point in time, the only cost that seemed important was the purchase and installation price of the pump. Today folks realize that purchase price is often only a small part of the overall cost of a pump, and other factors like warranty, installation/rigging, operating parameters, plant/facility alteration requirements, pump service and repair, and pump efficiency all factor into the total cost of ownership. In the pool pump, the decision was pretty simple with a low-cost motor replacement solution. In an industrial application, a pump issue decision is more complicated, and the associated costs can run into tens of thousands of dollars and more.

Examining Cost to Repair Pumps vs. Cost to Replace

Recently, the regional Water Pollution Control Authority in Waterbury, Connecticut, reached the point where major mid-life service was required on all four of their Allis Chalmers Model NSYV 250 Influent pumps. The pumps had been in service for 19 years and were showing signs that major service would be required in the near future. The City of Waterbury employed the professional engineering services of Tighe and Bond to develop proposals and assist in managing the project for the sequential overhaul of the pumps, motors, drive shafts and discharge check valves over a 12-month span. The technical and price evaluation resulted in the project award to New England Pump and Valve Company (NEPV). Many factors are taken into consideration when it comes to performing a job of this type and there are typically two perspectives that weigh heaviest. The pump owner is usually looking at the following factors in a service provider: knowledge and experience

• the provider’s resources (technical, financial, and workforce) to complete the work as proposed
• the relationships within complementary industries required in order to complete
• the work
• their professional reputation

Technically the pump owner is weighing the costs to repair versus to replace. Some of these considerations include: new versus overhaul costs, new pump system modification costs, parts obsolescence and original equipment manufacturer (OEM) support, and energy efficiency gains. Sometimes, a pump housing or casing may be so unique that refurbishment and repair is the only way to go. Even though the technology exists today, years after the original installation a different type of pump might perform the same function in a much simpler way. Lastly, often the equipment required to rebuild some larger pumps is not found in today’s standard machine shops. Studies of large pump efficiency have become popular due to the potential for significant cost savings. The City of Waterbury recognized the potential to reduce total ownership costs while completing this major overhaul project and partnered with the local electrical provider Eversource Energy to reduce energy consumption. The project is comprehensive and rigorous in approach to ensure the customer achieved all of their objectives including the following major project components.

• Performance testing (pre- and post-overhaul) that included pump and motor energy consumption and efficiency
• Vibration testing (pre- and post-overhaul) that is critical to optimizing pump and motor function and life. This also validated the dynamic balancing of the pump, motor and driveshaft
• Inspection and completion reporting for all major components including the pump, motor, driveshaft and check valve

A major focus of the energy savings was to incorporate a low resistance, durable ceramic epoxy coating on the interior flow surfaces of the pump. These coatings are field-proven technology to lower energy consumption by reducing flow friction as well as extending pump life by reducing corrosion and erosion of interior surfaces. The pump work consisted of:

• Pump casing: Sandblasting of both interior and exterior. The interior of the volute was then coated with ceramic coatings.
• Impeller improvement: The original impeller was still within spec and in good condition. It was sandblasted and coated with ceramic coatings. The impeller assembly (impeller, key, shaft, and nut) was made using thread lockers for proper fit. This technique prevents movement and potential vibration sources, and to insure no corrosion occurs in between the threads should future work on the pump be required.
• Pump system overhaul: Replacement of parts including bearings, seals, split mechanical seal, wear rings and shaft sleeve. Moderate shaft wear grooving was welded, machined and dynamically balanced with the impeller. All tolerances were restored to factory specifications and the exterior surfaces coated with a two-part epoxy.

Conclusion

So what did the test results show in this rebuild? An average efficiency improvement of 6 percent, and significant improvements in both pump head/flow and maximum flow rates. The targeted 2 percent energy reduction for this 250 horsepower (hp) motor-driven pump was exceeded, and these results are in line with prior studies by federal, state/local and industry groups. This is expected to expand as the work on the three remaining pumps is completed. The key to the success of this project and the efficiencies gained in the equipment performance are tied to the expertise of the service provider and their ability to properly select, prep and apply the correct ceramic coatings to meet the need. Rigorous oversight and documentation of the project by the design team ensured that the project goals were measured and achieved. So when faced with what may appear at first to be a negative situation, seek out the right solution coupled with the correct solution providers and it is likely the outcome will be a positive one.