Patent ID: 7389889

Claim:
A hoisting mechanism comprising: a. a frame; b. a jib connected to the frame about a substantially horizontal pivot shaft; c. topping means for raising and lowering the jib; d. a hoisting cable and a hoisting-cable drive; e. hoisting-cable guide means that define a path for the hoisting cable between the hoisting-cable drive and a hoisting-cable guide arranged on the jib, from which the hoisting cable hangs downwards; and f. a device for limiting the loading on the hoisting mechanism, comprising: i. a hoisting-cable guide for the hoisting cable, wherein the hoisting-cable guide is displaceable with respect to the frame or the jib, wherein the displacement of the hoisting-cable guide changes the length of the path; ii. a first hydraulic component arranged between the frame or jib and the displaceable hoisting-cable guide, wherein the first hydraulic component comprises a first chamber of a first variable volume; iii. a second hydraulic component comprising a second chamber with a second variable volume; iv. a pressure source connected to the second hydraulic component in order to maintain a substantially constant hydraulic pressure in the second chamber; and v. a connection between the first chamber and the second chamber, wherein the connection comprises a pressure-limiting valve assembly and actuating means, wherein the actuating means detects pressure in the first chamber.