Sequence of Operations |
Sequence of Operations |
Downcoiler HPU Off - Energy Stored in Accumulators |
It is standard practice at the Hot Mill to turn the electric motors that power the pumps off while keeping Solenoid Vented Relief Valve 261.02 for the Low Pressure Pump Group and Solenoid Vented Relief Valve 261.03 energized to their high pressure settings.
As a result, Accumulator 245 in the P1 pressure header line (the header line served by the Low Pressure Pump Group) is not vented to low pressure, and stored hydraulic energy is present in the P1 pressure header line. In order to vent the stored energy in Accumulator 245, Shutoff Valve 094.02, located on the manifold under the accumulator, must be opened. Listen as the stored fluid vents to tank through the opened shutoff valve. Attach a suitable pressure gauge to test point location M3 to verify the pressure has been vented.
The P2 pressure header line also contains several accumulators. Specifically, the Wrapper Roll circuits and the Top Roll Positioning circuit both include accumulators which keep P2 pressurized until all of the accumulators are manually vented. In addition, the Coiler Mandrel circuits each have two accumulators which store energy until they are manually vented. While a check valve located in the pressure line to each of the coiler circuits is supposed to prevent pressure stored in these accumulators from flowing back into the P2 pressure header line, if the check valves are not sealing properly, pressurized fluid will indeed flow back into the P2 pressure header line.
It must also be noted that in any circuit in which an actuator (cylinder) supports a load, there is pressure trapped between one end of the cylinder and either the directional control valve or a load control valve (a pilot operated check valve or a counterbalance valve). Before disconnecting lines connecting these cylinders to their control manifolds, ensure the load is adequately supported so induced hydraulic pressure is no loner present.