Overload protection devices can be divided into automatic stop type, alarm type and comprehensive type according to their functions.

The automatic stop overload limiter can stop the crane from continuing to move in an unsafe direction when the lifting weight exceeds the rated lifting capacity, and at the same time allow the crane to move in a safe direction. The safe direction refers to the descent of the lifting load, the retracting of the boom, the reduction of the amplitude and the combination of these actions. The automatic stop type is generally a mechanical overload limiter, which is mostly used on tower cranes.

The alarm-type overload limiter can display the lifting capacity, and can send out an alarm sound and light signal when the lifting capacity reaches 95% to 100% of the rated lifting capacity.

The comprehensive overload limiter can send out an alarm sound and light signal when the crane reaches 95%~100% of the rated lifting capacity. When the lifting weight exceeds the rated lifting capacity, it can stop the crane from continuing to move in an unsafe direction.

According to the structure, the overload limiter can be divided into three types: mechanical, hydraulic and electronic. Mechanical overload limiters include lever type and bullet type.

The overload protection device is designed to consider the influence of the crane’s apparent load. Under the conditions of lifting, braking, and vibration, the speed change will produce an additional load, and the lifting dynamic load often reaches 110%~130% of the rated load. . Dynamic load is an inherent dynamic phenomenon of lifting operations, and is a feature of hoisting machinery operations. Therefore, the overload protection device has designed a delay circuit based on this feature to make it have the ability to judge and deal with such false loads, while preventing actual If the load exceeds the specified value, malfunctions will not occur.