The overheating coal barge problem was caused simply from the lack of documentation and instructions on how to set the different pressures.
The pump compensator was set to provide enough force to pull the loaded barge through the un-loader system, and the safety relief was set properly at about 150 psi higher to protect the pump and system from excessive pressure spikes. These changes helped lower the heating problem.
When the feed-out valve was energized to allow the barge to drift down stream, the pulling cable hydraulic motor became a pump. The cable tension valve’s pressure should be set low enough to allow the barge to drift downstream without allowing it to run away. It operated somewhat like a counterbalance valve would on a cylinder.
The drifting barge pulling on the cable caused the hydraulic motor to act as a pump. Pumps need a suction line, and providing a small supercharge of 100 to 200 psi will prevent cavitation to the pump-motor unit, extending its operating life. Another benefit is that noise is greatly reduced by having a charged suction line.
However, the supercharge flow control was set way above the amount of oil lost to leakage. The excess flow was relieving over the supercharge pressure control, generating unwanted heat. To add to this problem, the supercharge relief was set above 400 psi.
After lowering the supercharge relief to 100 psi, the supercharge flow control was set as low as possible, just above the oil leakage rate. Lowering the valve to 100 psi also caused the differential pressure across the cable tension valve to increase by 300 psi. An adjustment was made to lower its setting by this amount. The system now operates normally.
Solution to October’s gold ladle tilting problem
The gold ladle system circuit that used the pilot operated directional valve with pilot chokes did not have any defective components. When our Jon Rhodes arrived to troubleshoot the problem, he noticed the pilot choke adjustment screws were adjusted to the fully extended position, (fully counter-clockwise). He told them the first thing they needed to do was open the pilot chokes by adjusting the screws fully clockwise. The clockwise adjustment actually opened the chokes. The illustration shows how the check controls speed in one direction and by-passes in the other. This is not an uncommon set-up and should be considered when troubleshooting systems.