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An ideal block and tackle with a moving block supported by n rope sections has the mechanical advantage (MA), = =, where F A is the hauling (or input) force and F B is the load. Consider the set of pulleys that form the moving block and the parts of the rope that support this block.
The ideal mechanical advantage of the block and tackle is equal to the number of sections of the rope that support the moving block. In the diagram on the right, the ideal mechanical advantage of each of the block and tackle assemblies [7] shown is as follows: Gun tackle: 2; Luff tackle: 3; Double tackle: 4; Gyn tackle: 5; Threefold purchase: 6
The name comes from the fact that the arrangement of lines is roughly Z-shaped. Besides the mechanical advantage to pulling, it also uses only part of the total length of the rope for the block and tackle arrangement. The typical configuration (see diagram) uses two single pulleys and two Prusik knot loops or other suitable friction hitches. [2]
Crown block (#13) is the stationary end of the block and tackle. Degasser (not pictured) is a device that separates air and/or gas from the drilling fluid. It is typically mounted on top of the mud tanks. Derrick (#14) is the support structure for the equipment used to lower and raise the drill string into and out of the wellbore. This consists ...
By looping more ropes around more pulleys we can construct a block and tackle to continue to increase the mechanical advantage. For example, if we have two pulleys attached to the rafter, two pulleys attached to the weight, one end attached to the rafter, and someone standing on the rafter pulling the rope, we have a mechanical advantage of four.
A traveling block is the freely moving section of a block and tackle that contains a set of pulleys or sheaves through which the drill line (wire rope) is threaded or reeved and is opposite (and under) the crown block (the stationary section).
In sailing, a block is a single or multiple pulley. One or a number of sheaves are enclosed in an assembly between cheeks or chocks. In use, a block is fixed to the end of a line, to a spar, or to a surface. A line (rope) is reeved through the sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle.
Crown block. A crown block is the stationary section of a block and tackle that contains a set of pulleys or sheaves through which the drill line (wire rope) is threaded or reeved and is opposite and above the traveling block. [1] [2]