In a educational video for kids about pulleys, a device named a chain pulley was mentioned, which was supposed to keep the load up without having to pull on it continuously (like with a tackle and block). I find this hard to believe (especially since the load shown was a mammoth :-). I suppose it's really a friction device of sorts, but the video was rather short on explanations. I haven't found a description on the web either.
...part of a standard chain hoist setup. Commercial chain pulleys, also called chain hoists, are designed to lift very heavy loads up to 25 tons safely. To do this they include a brake assembly to prevent the load from coming back down until you are ready for it and release the brake. Probably a good idea when lifting loads as heavy as chain hoists can deal with. A pulley designed to accomodate a chain will have a gear-like appearance where each link in the chain fits into a pocket in the pulley wheel. This prevents the slippage that can occur when using ropes or cables in a pulley system. Chain hoists are fairly standard equipment in industrial situations, they are a relatively small and inexpensive hoist that can lift very heavy loads by hand and can be used in small spaces that can not accommodate a crane. Considering the average weight of a mammoth was around 8-10 tons, a chain hoist could indeed lift one.
it looks like there is a locking mechanism within the pulley that keeps the wheel with the teeth that fit into the links of the chain from going backwards.
