An older four-post vertical press with a 6-ft daylight opening was designed with one cylinder on each corner of its platen. The cylinders extended to close the press and retracted to open. To keep the platen somewhat square and parallel with the press’s bed plate, a four-section gear-type flow divider was used to feed the cap end of the four cylinders.

Unfortunately, the plant’s maintenance crew had to replace the flow divider about once a month. The flow divider would crack at any one of the gear housing rings, and there wasn’t any pattern to which ring failed.

The crew was told to lower the press to the fully closed position and install a new flow divider. Sometimes the flow divider failed even before the crew finished bleeding air from the cylinder lines.

All hydraulic functions of the press were powered by a pressure-compensated piston pump set at 2,500 psi. The system’s safety relief valve was set to open at 2,750 psi, and the flow divider itself was designed to operate safely at pressures to 3,000 psi.

The flow divider circuit used a three-position closed-center directional valve with a limit switch to detect if the press drifted down 1 to 2 in. from full open. When this did occur, the limit switch would shift the directional valve to return the press back to the full-open position and hold it there for about 10 sec. The directional valve then would shift back to the center position.

Other than a few leaking fittings, the press seemed to be well maintained, so why was the flow divider failing so frequently?


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