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 complained 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 www.cfc-solar.com for more information.
Find the solution
Think you know the answer? Submit solutions to email@example.com. The correct answer will be published in the next edition of “Troubleshooting Challenge.”
All correct solutions will be entered for a chance at a $50 gift card — we will randomly select a winner from all correct answers. The winner’s name will be printed in the next edition of “Troubleshooting Challenge.”
The military project, with the 60-gpm pump and 40-hp electric motor, had two problems. The first was the lack of pressure. A load-sense compensator needs external pilot pressure to function above the original 300-psi load sense spring setting. The pressure needed to move a cylinder is fed to the load-sense spring chamber and is additive to the spring. The control orifice was probably blocked with contaminants, but the pump was still okay because the spring could increase the pressure to its limit of 500 psi.
The second problem with the leaking return line filter is a common problem when the return flow from the cap end of the cylinder is intensified due to the area ratio of the cylinder. If you divided the cap-end area by the rod-end area and multiplied the quotient by the pump flow going into the rod side, you would determine the flow leaving the cap end and going through the filter. A 2:1 area cylinder would result in a 120-gpm flow through the directional valve, filter, and heat exchanger. The contractor needed to find out the cylinder areas and determine if the components were rated for the return flow.
Spin-on element threads tend to stretch, making it feel like the element is loose. You can turn the element about 1⁄16 to 1⁄8 of a turn, and it will feel tight. Shortly after running the system, though, the element will start leaking again and can be tightened again. However, the stretched stud the element is attached to could break or the element threads could strip, causing the assembly to blow apart.