Manitowoc Published 11-22-17, Control # 257-02 5-17
MLC300 SERVICE/MAINTENANCE MANUAL HOISTS
Brake Defeat Valve
When the hydraulic system is operating properly, the
pressure on the A side of the motor should always be above
5 bar (73 psi).
The brake defeat valve (22) overrides the brake release
solenoid valve (14) to do the following:
• Prevent the brake from releasing (when applied) if
pressure on the A side of the motor is below 5 bar (73
psi)
• Apply the brake (when released) if pressure on the A
side of the motor drops below 5 bar (73 psi)
High Pressure Protection
The relief valve (10) protects the hydraulic pump (3) and
motor (18) from a pressure spike such as might occur when
bringing the boom to a sudden stop. The relief valve is
factory set at the specified pressure.
Drum 4 Cavitation Protection
When needed, the makeup check valves (19) open to allow
fluid stored in the makeup accumulator (20) to enter the low-
pressure side of the system, thereby maintaining a positive
pressure at the motor A port.
Drum 4 Motor Case Protection
The thermal expansion accumulator (21) connected to the
motor case protects the motor from damage due to thermal
expansion during drum storage/transport. If the pressure in
the motor increases, the pressure is captured in the
accumulator.
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