Hydraulic System Parking brake function Opening the brake The shuttle valve block directs the pilot control pressure to the SH input if rotation, boom swivel or dipper arm retraction is carried out. The pilot control pressure at the SH input causes the piston in the parking brake valve to shift to active state (brake vent). This directs the pilot control pressure at the PG input to the brake cylinder and vents the brake.
• Movement: rotation, boom swivel or dipper arm retraction. • Pilot control pressure is present at the SH input. • The piston of the parking brake valve moves to work position. • Pilot control pressure is directed to the brake piston. • Brake is vented. Closing the brake The shuttle valve block causes the pilot control pressure to drop and the SH input is not pressurized upon termination of rotation, boom swivel or dipper arm retraction. The piston in the parking brake valve switches to home position (brake) if there is no pressure at the SH input. The pressure in the brake cylinder escapes using the parking brake valve to the leak oil system. This enables the brake with some delay (depending on oil viscosity and brake valve leakage).
• End of movement: rotation, boom swivel or dipper arm retraction. • The pilot control pressure at the SH input drops. • The piston of the parking brake valve moves to home position. • No more pilot control pressure on the brake piston. • The oil in the brake piston flows to the tank using a throttle orifice. • The brake is enabled. Time for venting the brake: 3.7 sec +/-1.2 @ 122 °F (50 °C) oil temperature
5-30
918175/AP0605
