Pulleys and Blocks

General information

• A pulley is a wheel with a grooved rim in which a pulled rope or cable can run to change the direction of the pull and thereby lift a load.  Pulleys are found in blocks (a block is a case with one or more sheaves/pulleys).
• When using a pulley or block, it’s important to ensure the size of the sheave matches the size of the cable or rope being pulled through.  If there is a mismatch in size, damage can occur – not only to the rope/cable, but also the sheave.
  • If the sheave is too small, the rope/cable may be damaged through pinching, it may get stuck and introduce a magnified amount of tension at the block, it can dramatically heat up the block and cause heat related damage, and it may wear the sheave such that it becomes unsuitable for the originally intended size
  • If the sheave is too large, the rope/cable may be damaged through crushing and flattening, and it may wear a narrow groove in the sheave that can damage ropes/cables of the originally intended size
• As a rule of thumb, the diameter of a pulley should never be less than 5 times the diameter of the rope (so as to reduce the potential damage caused by sharp turns relative to the rope/cable’s size).
• Pulleys/blocks must be properly lubricated in order to avoid wear and heat
• If there is damage to the sheave, it should be taken out of service as it may damage the rope/cable with each revolution.