Coupling Redesign, Alignment, help Smooth Pump Operation

A Florida water treatment plant recently discovered that having full-flex (double engagement) gear couplings at either end of a spacer shaft connecting a Lufkin gearbox to a 13,000 gpm Worthington water pump caused self-exacerbating vibration that eventually destroyed the gearbox twice within 3 months, requiring a full rebuild each time.

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A Florida water treatment plant recently discovered that having full-flex (double engagement) gear couplings at either end of a spacer shaft connecting a Lufkin gearbox to a 13,000 gpm Worthington water pump caused self-exacerbating vibration that eventually destroyed the gearbox twice within 3 months, requiring a full rebuild each time.

After the second rebuild and re-installation, Ludeca was called in to monitor positional changes between the stopped and running conditions of the entire diesel engine-driven machine train with its Permalign system to derive true target specifications for the "cold" condition. Thereafter, a laser re-alignment to exact tolerances would be performed to the new targets.

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The existing system design resulted in gearbox failure twice in three months

Upon arrival, Ludeca technicians discovered the facility was using full-flex gear coupling hubs on machine shafts and also on a spacer shaft.

At their suggestion, the couplings were replaced with single engagement gear couplings at either end, with the floating hubs on the outboard ends to maximize the permissible misalignment while still meeting tolerances. The realignment to targets was successfully performed, and subsequent vibration studies showed a significant reduction.

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Installing single-engagement gear coupling hubs with flex hubs on machine shafts corrected the problem. A realignment with a Rotalign Ultra tool helped minimize vibration.

The machine train has now been operating over a year, approximately 18 hours per day, without problems. For more information on the Ludeca alignment systems, visit www.ludeca.com.

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