What are the types of limit devices that tower cranes must have?

Tower cranes must be equipped with several types of limit devices, including: 1. Load Limiter: Also known as an overload limiter, it is a safety device that prevents the crane from operating beyond its load capacity. When the lifting weight exceeds the rated lifting capacity, it automatically cuts off the power supply to the lifting mechanism to stop or issue an alarm. Load limiters come in two types: mechanical and electronic. 2. Moment Limiter: For variable jib cranes, a certain jib length only allows lifting a certain weight. If the weight is exceeded, there is a risk of the crane overturning. The moment limiter is a protective device developed based on this characteristic. At a certain jib length, if the lifted object exceeds its corresponding weight, the circuit is cut off, preventing the lifting process and ensuring the stability of the crane. Moment limiters come in three types: mechanical, electronic, and composite. 3. Height Limiter: Also known as a hook height limiter, it is usually installed at the head of the lifting arm. When the hook rises to the limit position, it lifts the lever, pressing the limit switch to cut off the circuit and stop the crane. When the circuit is re-closed, the hook can only descend. 4. Travel Limiter: A safety device to prevent the crane from colliding or restricting its travel within a certain range. It is generally installed on the inside of the active trolley, mainly consisting of a travel switch with a movable lever. Additionally, a fixed limit stop is installed at the end of the track (at the restricted position of travel). When the tower crane travels to this position, the limit stop touches the lever of the travel switch, cutting off the power supply for the travel control. When the circuit is re-closed, the tower crane can only operate in the opposite direction. 5. Jib Limiter: Also known as a jib limiter or jib indicator, boom cranes have a jib indicator hanging on the lifting arm. It consists of a fixed circular indicator disc with a vertical movable pointer at the center. When the jib is adjusted, the pointer indicates the rated lifting weight at various jib lengths. When the jib reaches the upper and lower limit positions, it presses the limit switches, cutting off the main control circuit, and the jib motor stops, achieving the limiting function.