Pumped up

Universal power frame cartridges provide maintenance and reliability benefits to centrifugal pumps

by David R. Mikalonis

Problem: When a major pulp mill recently took stock of an aging population of centrifugal pumps installed over a number of years, the numbers foretold potentially daunting maintenance headaches and costs.

The mill counted more than 400 pumps, 15 brands, 25 models and 40 different power frames. The inventory of shafts, sleeves, bearing sets and mechanical seals was enormous. Some models had become obsolete, several were classified as �bad actors,� many required costly replacement parts, and others had limited service and parts availability.

Solution: An upgrade program was initiated to replace all the power frames in an orderly progression over time using universal power frame cartridges complete with bearings and mechanical seals and able to fit existing pumps. This proactive approach left pump volutes in place and avoided any need for pump replacements or changes to piping or foundations.

Results: The mill�s entire pump population could be accommodated with three frame sizes, dramatically reducing inventory of spare parts and frames (from $5 million to $1 million), and contributing to increased reliability and pump service life attributed to the frame�s design and engineering.

Fears of failure
As the mill example suggests, pump designs have changed little over the decades, and users typically anticipate from experience that pumps will fail sooner rather than later and at considerable cost. Across industry lines, pump rebuilding programs and parts replacement make routine work for maintenance departments. But such routines can carry a high price when maintenance staffs must spend time, money and energy in ongoing �fixes.� Unanticipated downtime negatively impacts productivity, and escalating costs for repair parts undermine profitability.

Primary culprits in most ordinary centrifugal pump failures are the bearings and mechanical seals. Root cause of the failures typically can be traced back to heat and vibration.

Developed as an easily retrofitted mechanical assembly, �self-contained� universal power frame cartridges in sturdy one-piece housings offer optimized protection against failure for bearings and seals, in turn boosting reliability, pump service life and uptime. Cartridges meet ANSI and API pump specifications, and three basic frame sizes fit virtually all the pump brands and models (helping to reduce replacement inventory).

A word of advice: Be sure a power frame cartridge comes standard with a comprehensive warranty for multiple years to contribute to peace of mind and cost-effectiveness.

Looking inside
Bearing arrangements for these power frames consist of a duplex pair of high-capacity, single-row angular contact ball bearings situated back-to-back and positioned closer to the impeller in order to:
� accommodate high loads and reduce vibration;
� improve running accuracy, shaft stiffness and seal stability;
� reduce the effects of axial expansion on process efficiency;
� eliminate bearing misalignment;
� and, eliminate the need for cold/hot impeller clearance adjustments.

The hydraulically double-balanced, self-adjusting stationary design of their mechanical seals enables universal power frame cartridges to operate from full vacuum to 400 psig pressure. Concentric seal technology delivers maximum cooling and seal-face lubrication, and multiple seal positions provide a built-in backup system for added protection and longer power frame service life. No seal adjustments, settings or measurements are required upon installation, saving time and money.

Cartridges can be readily converted from standard power frame to hermetically sealed units to contain process fluids in the power frame, minimizing costs of leak detection and repair. Seal arrangement flexibility allows one modular design to handle a wide range of liquids and slurries.

Making life easier for maintenance staff during installation, the cartridge�s thick-walled housing design allows the use of C-frame adapters with motor horsepower up to 200 hp to provide immediate alignment of the motor and pump. These �drop-in replacement� units can be bolted easily into place on the existing pump�s �wet end� without modifying pump, piping or foundation. No seal adjustments, settings or measurements are required. Interchangeable shaft ends can fit any impeller configuration.

Real-world casebook
Every industry has its own requirements for pumps and every facility will have its own unique operating conditions and demands. However, here are a few more examples:

Wastewater treatment industry: A Massachusetts wastewater utility routinely experienced excessive noise, vibration and leaks pumping viscous and high-solid fluids. Slurry pumps were upgraded with universal power frame cartridges, which fit the old horizontal-recessed impeller slurry pump perfectly. Now, the pump operates quietly and with little vibration.

Brewing industry: One of America�s largest breweries ran exhaustive tests to determine whether universal power frame cartridges could reduce inventory costs, increase uptime and decrease maintenance. Because the components are backward compatible with the brewer�s installed pumps, retrofitting was seamless. This compatibility allows it to reduce expensive storeroom inventories that it was required to stock in order to cover all of the pump manufacturers. Stocking universal parts offered substantial savings.

Paper industry: A leading U.S. paper producer using hazardous formaldehyde in its process sought to install the best possible equipment for this critical pumping application. (Leaks can lead to serious environmental issues.)  Top priorities were a key-driven, stationary-spring, double-balanced mechanical seal design and an enclosed housing. With universal power frame cartridges, the mechanical sealing solution operates flawlessly and the fully enclosed frame design adds an extra measure of protection.

David R. Mikalonis is the global program manager for SKF USA Inc. To learn more, call or e-mail . 

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