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Crane (Machine for lifting weights)

a machine for lifting weights, worked either by hand, or by steam, or by hydraulic power. The most common hand form consisting of an upright revolving post and a projecting arm (usually at an angle of about 45°), the jib with a fixed pulley at its extremity.

Whenever much hoisting or heavy work has to be done, steam or hydraulic power is always used; the cranes are then either stationary or portable, the latter type being used whenever it is more convenient to move the crane to its work than the converse. The stationary power cranes differ from the hand ones mainly in their vastly greater power, and consequently greater size and complexity of gearing; where steam is used there are generally two direct-acting steam-cylinders, which replace the two handles worked by hand.

The very powerful stationary cranes used in docks capable of lifting 50 to 75 tons are examples of this kind. Hydraulic power is very largely used in cranes for these places and in great steel-works; they are simpler in construction, a good deal of gearing being done away with; the water in the operating cylinder is always under great pressure.