EXPERT COLUMN | LEEA
Mechanical advantage for lifting and pulling
loads need to be moved, raised or positioned safely and efficiently. Using a gripping action on wire ropes, they can lift and lower loads to a distance limited only by the length of rope. Applying mechanical advantage in this way, the machines make it easier to lift or pull a heavy load to reduce manual effort and improve safety. In addition to being used as permanent
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installations, the machines are frequently useful as a portable appliance and have become essential items of lifting equipment. Examples of uses include moving and placing building materials on a construction site, tensioning and placing utility poles, loading and unloading ships in docks and lifting equipment in factories. Some applications will use more than one machine, such as when they provide a means of tensioning in the guying of towers. There are two main types of lifting and pulling machines. Manually operated machines have a hand-operated lever to activate a mechanism that provides a direct pull on an integral rope attached to the load. The pull is applied by two pairs of self-energising jaws, which exert a grip on the rope. Powerful springs provide the initial pressure, causing the jaw to grip the rope and give the self-energising action. Hydraulically operated machines have an
integral hydraulic mechanism to provide power. These machines can be used as a single unit or ‘ganged’ units with the addition of a purpose- designed hydraulic system approved by the competent person or manufacturer. When it comes to selecting a lifting and pulling machine, always consider the safe working load (SWL). For lifting applications under normal operating conditions without any hazards, the SWL will be the same as the rated capacity. The rated capacity should be based on a minimum safety factor of 5:1. This applies to the machine, the rope and the terminal fittings. For pulling jobs, the manufacturer may permit a lower factor of safety of 3:1 to give a higher working capacity, so check their instructions. For people-carrying applications, the factor of safety
10 | May/June 2026 |
www.hoistmagazine.com
ifting and pulling machines, also known as jaw winches, are versatile pieces of equipment, widely used anywhere heavy
Ben Dobbs
Technical Committee
Ben Dobbs, head of global standards and legislation at the Lifting Equipment Engineers Association (LEEA), looks at the selection of lifting and pulling machines and how to use them safely.
of the machine, rope and terminal fittings should be increased to a minimum of 10:1. The SWL should not exceed 50% of the rated capacity. However, additional precautions are required and the LEEA Code of Practice for the Safe Use of Lifting Equipment (COPSULE) should be consulted for further guidance. The wire rope supplied for use is as integral
to the mechanism as a chain is to a chain hoist or lever hoist. Some ropes may not be suitable, even if they appear to be of the correct size and initially seem to be accepted by the machine. This is because the efficiency and safety of the friction grip of the machine’s jaws around the rope depends entirely upon the rope being of the right diameter and constructed to withstand the immense gripping power of the jaws. It is essential to use only ropes that have been approved and certified by the machine manufacturer as suitable for this use.
Safe use In addition to any specific manufacturer’s instructions relating to the safe use of these machines, there are several key safety factors to consider. The following factors are purely for wire rope machines and are only really specified as a ‘general rule’ in the legislation. They begin with ensuring the machine does not raise, lower or suspend a load greater than the SWL marked on it. If using multiple units, take care to ensure
that the share of the load taken by any individual machine does not exceed its SWL. Kinks must not be allowed to form in the rope. Practices such as incorrect unreeling and forming the rope into a sling or looped eye likely to cause kinks should be prohibited. Similarly, ropes with broken wires should not be used because it only takes one broken wire to jam in the machine’s mechanism and render it inoperative. Manually operated machines should only be used with a handle provided by the manufacturer. Under no circumstances should the handle be extended with tubing or bars to increase leverage. Generally, it should only require one person to operate a machine up to its SWL. If more are needed, it may indicate that the load exceeds the machine’s SWL. This does not preclude the use of two people to operate the machine, but it does demonstrate the degree of operating effort normally required. Never attempt to operate both raising and lowering levers at the same time – it is dangerous. A final piece of safety advice is that where overload prevention devices are fitted, their integrity must be maintained. Under no circumstances are they to be overridden. For example, if shear pins in the operating lever are fitted and if they fail, it is evident that the machine has been overloaded. Any measures to interfere with the operation and function of the pins is unsafe.
Training Training for using these machines should consider the manufacturer’s instructions for installation and use, and should pay particular attention to identification of correct wire ropes. In the case of machines used for temporary installations, the selection of suitable suspension or anchor points should be covered. LEEA’s COPSULE requires all operatives to be trained in the use of the equipment they will operate. It imposes a duty on them to use only equipment for which they have received training and to use it only in the manner for which they have been trained. It is recommended that formal training be undertaken and a record kept that the operative reached a satisfactory standard.
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