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A drum hoist (steel wire rope visible) and motor. In underground mining a hoist or winder [1] is used to raise and lower conveyances within the mine shaft.Modern hoists are normally powered using electric motors, historically with direct current drives utilizing Ward Leonard control machines and later solid-state converters (), although modern large hoists use alternating current drives that ...
Pulley in oil derrick A hoist using the compound pulley system yielding an advantage of 4. The single fixed pulley is installed on the hoist. The two movable pulleys (joined) are attached to the hook. One end of the rope is attached to the crane frame, another to the winch.
The difference in radii can be made very small, making the mechanical advantage of this pulley system very large. [4] [5] In the extreme case of zero difference in radii, MA becomes infinite, thus no force (besides friction) is needed to move the chain, but moving the chain will no longer lift the load.
An air winch, sometimes known as an air hoist or air tugger, is an air-powered version of a winch. It is commonly used for the lifting and the suspension of materials. In the oil and gas, construction , and maritime industries, air winches are frequently preferred to electric, diesel, and hydraulic winches because of their durability ...
In this way the boom moves at the same speed as the winch veers the topping end of the halyard and hauls the lowering end of the halyard, and vice versa. The slewing ends are also wound on to another half-barrel. There is a third winch to hoist to cargo on the yoke. Runners decrease swing and rotation of the cargo.
Vitruvius, a military engineer writing about 28 BC, defined a machine as "a combination of timber fastened together, chiefly efficacious in moving great weights".About a century later, Hero of Alexandria summarized the practice of his day by naming the "five simple machines" for "moving a given weight by a given force" as the lever, windlass, screw for power, wedge, and tackle block (pulley).
The Roman Polyspaston crane, from Ancient Greek πολύσπαστον (polúspaston, “compound pulley”), when worked by four men at both sides of the winch, could lift 3000 kg. In case the winch was replaced by a treadwheel, the maximum load even doubled to 6000 kg at only half the crew, since the treadwheel possesses a much bigger ...
The first of these systems used mechanical clutches between luffing and hoist drums, giving simplicity and a "near level" result. [5] Later systems have used modern electronic controls and quickly reversible motors with good slow-speed control to the hoist winch motors, so as to give a positioning accuracy of inches.