Lifting heavy objects can be frustrating and even dangerous. Lifting jacks, lift tables, motorised hoists, cranes and other specialised lifting equipment can be expensive. The Bureau of Labor Statistics (BLS) reports that sprains, strains and tears -- including lifting injuries -- account for nearly one-half of annual reportable injuries in the workplace. Heavy objects can be lifted safely and cost effectively with pulley systems.
- Skill level:
Things you need
- Lifting slings
Weigh or estimate the load weight of the object to be moved. Obtain lifting straps rated for more than twice the load weight as a safety factor. Slings may be chains, wire rope or synthetic rope or slings, depending on the materials to be lifted. Rig the load with the lifting straps to provide a balanced lift.
Measure the vertical height needed for the lift. This will be the distance needed to move the object using pulleys from one floor to another as an example.
Calculate the mechanical advantage and velocity factors needed for the lift. The mechanical advantage increases for each pulley added. Adding two pulleys doubles the mechanical advantage.The velocity factor decreases by the same amount. If you need to lift 454kg. and you have a maximum effort available of 45.4kg., you will need 10 pulleys to lift the load. You will also have to move 10 feet of rope for every foot of lift. You will need 100 feet of rope to lift 10 feet with a velocity factor of 10 as an example.
Locate the top pulley attachment point at a height above the final elevation that includes as a minimum the height of the object being moved and the pulleys used to lift it. Adding height to the attachment point will give you more flexibility in the lift and only require additional rope.
Attach the pulleys to the top pulley attachment point and the load. Use slings or cables to attach the load to the lower pulleys. One-half of the needed pulleys will be attached at the top pulley attachment point and one-half will be attached at the load lifting point.
Secure all pulley connections. Run the rope back and forth through the upper and lower pulleys. Secure the end of the rope at the top attachment point or on an attachment point found on the base of some pulleys. Leave enough rope to reach the ground or level you will be using to pull the load.
Test the load to ensure it is within your lifting limits. If you cannot safely lift the load, add more pulleys in sets of two to gain additional mechanical advantage. Obtain a longer rope if pulleys are added due to the lower velocity factor that results.
Tips and warnings
- Wear gloves when using pulleys and ropes to prevent hand injuries if the rope slips.
- Always lift slowly when you begin to ensure your slings have the load properly balanced. Stop and balance the load if it shifts suddenly or begins to swing.
- A separate rope attached to the load and handled by a safety person can keep a load from swinging.
- Never stand under a load you are lifting. Provide enough rope to stand well to the side. Barricade lifting areas to prevent others from walking under any lift.
- Ropes, cables and slings will show wear each time you use them. You should carefully inspect all equipment used in lifting before each lift.
- Never wrap ropes around your wrists when lifting; if the load begins to fall the rope can sever your hand.
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