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A progressive die press was designed to form shell casings for use in military tanks.
The circuit shown is for the main press, which was designed to meet a minimum cycle time. The machine performed well during test runs, with the customer observing the results. The press was disassembled before being shipped overseas for operation.
After it was reassembled and running, it started to cycle slower than the designed cycle time. The press manufacturer instructed the operator on adjusting the hydraulic system’s counterbalance valve, but that did not help. The operator also confirmed that the tank line of the relief valve was not warm to the touch. A warm or hot tank line would be an indication that the relief valve was leaking.
In addition, the operator installed a flow meter on the main pump’s case drain, but flow was well within the normal range. Next, solenoids 2A and 3B were energized with the press cylinder fully extended. It was determined that no leakage occurred over the logic valve.
Finally, they opened NV-1 valve, which controls the shifting speed of the directional valve. When shifting the valve to raise the press after it was up to tonnage, it resulted only in increased shock. The valve is rated to pass 45 gpm, which is why a logic valve is used when retracting the cylinder.
Any idea what could be causing the problem?
FIND THE SOLUTION
Think you know the answer to this month’s problem?
Submit your solution by emailing Mindy Timmer at [email protected]. All correct solutions submitted by January 5, 2016, will be entered into a random drawing for a $50 gift card. The winner will be notified, and his or her name will be printed in a future issue. Only one gift card will be awarded to any participant within a calendar year.
Congratulations to Andrew Thompson, P.E., of Climax Portable Machining & Welding Systems, Newberg, Oregon, who won November’s Troubleshooting Challenge by having his answer drawn at random from those who correctly solved that month’s problem. A $50 gift card was sent to him.
SOLUTION TO LAST MONTH's CHALLENGE
When the piston seal of a piston-type accumulator starts to leak into the gas area, it will increase the precharge pressure, which reduces the amount of oil the accumulator will hold. Repairing the accumulator and restoring it to the correct precharge resolved the problem with the slow mushroom lift.