A crane that can easily move around the job site with using own wheels and power is called a mobile crane. The movements of the mobile crane on the job site are called travel movements, while the movements from one job site to another are called transit movements. All mobile cranes can travel, except the crawler cranes. The upper framework of the mobile cranes is called upper structure, while the lower framework is called a carrier or a handler.
Today, there is an unofficial system used by many manufacturers for rating the mobile cranes, and this system is based on the lifting capacity. For example, a nominal rating of a 250 ton crane reflects the greatest theoretical load that crane can pick in any configuration. But, a heavy load that is constrained may be close to the boom and the cabin of the 250 ton crane. So, the nominal rating is just an irrelevant index for classifying mobile cranes.
The load ratings of the mobile cranes are commonly governed by their ability to resits overturning. The weight of a 250 ton crane provides a great resistance for overturning, but adding counterweights at the rear end of the upper structure increases the lifting capacity. Before adding counterweights, the operator needs to ensure that the 250 ton crane is secured from tipping over when short booms are used. Because there are road limitations, the counterweights are re-attachable and and cannot be mounted when the 250 ton crane is on the road.
The mobile cranes for sale have crane controls that function through electrical cables, pneumatic/hydraulic pressure and mechanical linkages. The drive systems enable the operators to keep the production rates very high. When a driver operates a car at top speed, great amount of power is needed for reaching the top speed, while decreasing the safety level. The same goes for a 250 ton crane, meaning that a responsible and careful behavior of the crane operator is essential.
