Pulley forces on the moving block must sum to zero. In addition the tension in the rope must be the same for each of its parts. This means that the two parts of the rope supporting the moving block must each support half the load. These are different types of pulley systems: The mechanical advantage of the gun tackle can be increased by interchanging the fixed and moving blocks so the rope is attached to the moving block and the rope is pulled in the direction of the lifted load. In this case the block and tackle is said to be
Lifting Operations and Lifting Equipment Regulations 1998 indicate safe working loads; ensuring that any equipment is positioned and installed so as to minimise risks; that the equipment is used safely ensuring that work is planned, organised and performed by a competent person; that equipment is subject to ongoing thorough examination and where appropriate, inspection by competent people. The regulations define lifting equipment as "work equipment for lifting or lowering loads and includes its attachments used for anchoring, fixing or supporting it". The regulations involve anything which involves the lifting of goods or people at work. Equipment covered would include lifts, cranes, ropes, slings, hooks, shackles, eyebolts, rope