A pulley block is a “block,” or series, of pulleys sharing the same axle. Multiple blocks are used in conjunction to achieve a mechanical advantage, reducing the amount of force required for some lifting task. One block attaches to the load while another block attaches to some immobile support. Because the line, or “tackle,” threads backs and forth between the two blocks, the line has to be pulled out a great deal in order to get the two blocks to come together a small distance. The payback is that far less force is required to lift the load.
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Things you need
- Two multiple-pulley blocks
- Line, string or rope
Purchase two pulley blocks. (See Resources for where to purchase mountaineering double-pulley blocks with eyelets online.)
Attach one of the two blocks to the load you want to lift.
Attach the other pulley block to a stationary support directly above the load, so that it hangs down, the pulley wheels oriented vertically. Get the rope or line to be threaded through the blocks. Call the front end that you’ll thread through the pulleys End A and the end that you’ll ultimately pull to lift the load End B.
Thread End A over one of the pulley wheels of the hanging double-wheel block. In other words, the line will make contact only with the upper half of the pulley wheel.
Thread End A down under one of the pulley wheels of the block attached to the load. In other words, the line will make contact only with the lower half of the pulley wheel.
Continue to thread End A up and down, over the top block’s pulleys and under the bottom block’s pulleys, until the pulleys all have tackle running through them. From the last block through which a pulley was available for threading, pull End A up/down to the other block and tie End A to it. (The double-pulley blocks listed in the Resources section have multiple eyelets to make this attachment.)
Pull End B to lift the load.
Tips and warnings
- The more blocks you use, the more times you’ll thread the line back and forth, and therefore, the more mechanical advantage you’ll gain. To put numbers to it, if the load is to be lifted 1 foot, then the load-mounted block also must rise 1 foot. Therefore, the distance between the two blocks must shorten one foot. If the line through the pulleys runs between the two blocks four times, then End B must be pulled out 4 feet to short these four stretches of line 1 foot each. The payout is that the force to lift the load one foot is only one-fourth the weight of the load.
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