Event: Thrust Block Cylinder - Retracting (Retract)

For previous sequences in this event see the event “Roll Change HPU – On.”

 

Note that this event describes the sequences for Mill Stand F1. The same sequences apply for stand F2 through F6, though the component numbers will change. Refer to the relevant schematic for each stand for the appropriate component number.

 

1)    Proportional Directional Control Valve 327.02 is energized to the parallel flow pattern allowing pressurized hydraulic fluid to flow through the valve passing from P to A. Next, the fluid flows freely through Pilot Operated Check Valve 163.03, then into the rod end of Thrust Block Cylinder 612.02 causing the cylinder to retract. The proportional directional control valve controls the retraction speed of the cylinder using both meter-in and meter-out flow control. Note that at the time this event was written, Thrust Block Cylinder 612.01 has been removed from the system.

2)    Exhaust fluid from the cap end of the cylinder flows freely through Pilot Operated Check Valve 163.04, which has been piloted open by pilot pressure from the A-side of the circuit.

3)    Finally, the exhaust fluid flows back to tank through the proportional directional control valve, passing from B to T, Check Valve 122.01 and Duplex Return Line Filter 045.01.

4)    Note that Pressure Relief Valve 284.03 protects the rod end of the cylinder from overpressure caused by external loads acting to extend the cylinder rod. Check Valve 159.09 provides makeup fluid to the cap end of the cylinder to prevent cavitation in the event this action occurs. By the same logic, Pressure Relief Valve 284.04 protects the cap end of the cylinder from overpressure caused by external loads acting to retract the cylinder rod. Check Valve 159.08 provides makeup fluid to the rod end of the cylinder to prevent cavitation in the event this action occurs.