Cleaning up the aftermath of Hurricane Katrina was a huge undertaking. Street sweepers were in great demand and used heavily to keep debris off the roads that were still passable. It was important to continually sweep nails and sharp objects that would fall off trash hauling trucks and flatbed trailers.

One contractor explained that his sweepers were breaking down frequently due to their hydraulic motor shaft seals failing. The part of the circuit for the brush motors is shown. The motor on the curb side seemed to fail more often than the one on the street side.

A manufacturer’s catalog stated that the sweeper’s hydraulic motor was “especially suited for low-flow, high-pressure applications.” It also stated: “High pressure Viton shaft seals eliminate the need for a case drain.” System pressure in the sweeper’s hydraulic system would fluctuate between 1500 to 2000 psi, and the rated continuous pressure listed in the catalog was 3000 psi. The system relief was set to 2400 psi. The catalog suggested a particular model for bi-directional applications, which was the case for this equipment.

At first, the contractor ordered shaft seal kits, then started ordering new units because he thought his maintenance people might not be installing the seals properly. But failures still occurred.

Any idea why the shaft seals were failing?

Robert J. Sheaf Jr., is founder and president of CFC Industrial Training, a Div. of CFC Solar, which provides technical training, consulting, and field services to any industry using fluid power technology. Visit for more information.