Event: Hold Down Roller - Emergency Mode

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

 

1)    In emergency operation Directional Control Valve 303.14 is energized to the crossover flow pattern allowing pilot pressure to pass through the valve from P to B. The pilot pressure pilots open Pilot Operated Check Valves 162.01, 162.02 and 161.25. By opening 161.25 reduced pressure fluid from Accumulator 236.03 may flow into the rod ends of Hold Down Roller Cylinders 652.01 and 652.02 thereby protecting the rod sides of the two cylinders. Makeup fluid may also flow through Check Valve 158.09 into the rods.

2)    Note that the pressure of the fluid supplied by the accumulator is controlled by Proportional Pressure Reducing Valves 277.01 and 277.02.

3)    Also note that the spool center of Proportional Directional Control Valve 333 is shown as a float center. Though the A and B ports are indeed open to tank when the valve spool is centered, due to the metering spool in this valve the flow through those connections is greatly metered when the spool is centered, metering any leakage to tank to a vast degree.