Crane safety devices: To ensure safe and reliable operation of lifting cranes equipped with better safety devices Wanted crane, so that in case of an accident, mechanical or protect Calls attention to the sale of used cranes, which play a security effect. Each hydraulic system relief: Can cause abnormally high pressure circuit used cranes to prevent damage to hydraulic pumps and motors, and to prevent an overload in the state. Crane safety devices: the height limit device. Hook from a predetermined height after the rise of second-hand crane market, touching the weight limit, open limit switch, 'had about' indicator light that is bright, and cut off the hook lifting, arm extended, the boom volts to, etc. to ensure safe operation of the operation. Then just manipulate the hook down boom boom retracted or lifted up (ie safe side operation), etc. When the handle so that the limit weight lifting constraints, normal operation is restored.