What types of limit devices must tower cranes have?

Tower cranes must be equipped with lifting capacity limiters, torque limiters, height limiters, travel limiters, amplitude limiters, etc.

(1) Lifting capacity limiter: also known as overload limiter, is a safety device that can prevent the crane from operating under overload. When the lifting weight exceeds the rated lifting capacity, it can automatically cut off the power supply of the lifting mechanism to stop or issue an alarm. There are two types of lifting limiters: mechanical and electronic.

(2) Torque limiter: For variable amplitude cranes, only a certain amount of lifting weight is allowed to be lifted. If it is overweight, there is a risk of the crane tipping over. The torque limiter is a protective device developed based on this characteristic. At a certain range, if the suspended object exceeds its corresponding weight, the circuit will be cut off, making lifting impossible and ensuring the stability of the crane. There are three types of torque limiters: mechanical, electronic, and composite.

(3) Height limiter: also known as hook height limiter. It is usually installed at the head of the boom, and when the hook slides to the limit position, it supports the lever. Press the lower limit switch, cut off the circuit to stop, and when closing again, the hook can only descend.

(4) Travel limiter: a safety device that prevents a crane from colliding or limiting its travel within a certain range. It is generally installed on the inner side of the active trolley, mainly equipped with a travel switch that can be toggled. Install a fixed limit position baffle at the end of the track (at the designated position during operation). When the tower crane reaches this position, the limit baffle will touch the lever of the travel switch, cutting off the power supply for controlling walking. When it is closed again, the tower crane can only run in the opposite direction.

(5) Amplitude limiter: also known as amplitude limit or amplitude indicator, the boom of a typical boom crane is equipped with an amplitude indicator. It is composed of a fixed circular indicator dial with a vertical movable pointer installed at the center of the dial. When the amplitude changes, the pointer indicates the rated lifting capacity at various amplitudes. When the arm reaches the upper and lower limit positions, press the lower limit switches respectively, cut off the main control circuit, and stop the variable amplitude motor to achieve the limit function.