A simple 2,000-psi hydraulic system was designed and installed to run a conveyor in a hog-processing plant (see schematic). Two belt conveyors at a vertical angle to each other create a V shape, with about a 12-in. gap at the bottom and about a 30-in. gap at the top. A flat floor at the bottom of the conveyor slopes down from the entrance. Hogs travel down single file into the conveyor. As they enter the conveyor, the sloping floor causes the hogs to be wedged in and carried to where they are dispatched, and processing begins.

The new system developed a problem with the C-face mounted pump shaft seal failing after six weeks or so. The seal lip with a garter spring was pushed out. The maintenance crew replaced the seal and was told by the power-unit builder that this type of failure was normally due to excessive pump case pressure. The crew installed a standard 0- to 300-psi pressure gauge teed into the case line to monitor case pressure.

They observed it for several hours, then every day for a week or two. They noticed that when the pump compensated each time the conveyor was stopped, the pressure would spike between 10 and 15 psi but then only read about 5 to 8 psi. When the directional valve was shifted to run the system, the pressure would drop even lower.

The pump shaft seal failed again five weeks later. The power-unit builder said case pressures this low shouldn’t cause these failures, but they did not know what could be causing the failures.

Do you have any ideas?

Read more: Troubleshooting Challenge: Shaft Seal Fails on Pressure-Compensated Pump