A limestone mine in Kentucky, reaching 1.1 miles below the surface, had overheating problems with a hydraulic system on a lift elevator. The lift was used for moving large equipment and workers in and out of the mine, which ran 24/7. Refer to the accompanying schematic for an overview of the hydraulic system.

The mine’s maintenance department determined from past experience their supply of water for cooling was in poor condition. Consequently, the hydraulic system’s four-pass water-cooled heat exchanger needed to be reamed out, cleaned, and resealed every six months. Technicians installed a reconditioned heat exchanger, but the hydraulic system was still running hot — even though swapping out the heat exchanger solved the problem in the past. They concluded something else was causing the excessive heat.

Technicians first checked a cooler-bypass check valve that was mounted separately. It seemed in good operating condition. A standby pump-motor unit was brought online, but switching to it did not solve the problem. Case-drain flowmeters and pump pressures on both units seemed to be fine.

They then surmised that the problem was probably in the motor circuit because it ran most of the time. A new hydraulic motor was installed, but the problem still persisted. Next, a new filter element was installed, but that didn’t help, either.

Finally, for some reason, they then replaced an accumulator. Of course, this did not solve the problem, so what do you suggest?

Editor's Note: The problem as printed in our August issue states that replacing the accumulator solved the problem. It did not, and we aplogize for any inconvenience this error may have caused.