“Give me a place to stand, and I shall move the Earth with a lever” – Archimedes, 3C, BC
The geometry behind the lifting theory of levers is attributed to Archimedes, although levers had been used for millennia before this. Today, we don’t need levers to lift huge weights. We have hydraulic cranes instead. Archimedes understood the importance of compound pulleys – which are one of the principles behind hydraulically powered harbour cranes. The eminently quotable mathematician went one further with his next challenge. According to Plutarch’s Life of Marcellus, Archimedes was challenged by King Hieron of Syracuse to lift a three-masted ship, laden with passengers and cargo, from the shore where it was dry-docked, into the water. Archimedes managed the feat single-handed, simply through the use of compound pulleys.
Modern Hydraulic Cranes
Because hydraulic cranes are compact, they are ideally suited to working in limited spaces, such as a harbour. The power of the compound pulley systems, combined with hydraulics, means that they don’t need the long boom arm of a traditional tower cranes, as the torque is transferred via hydraulic hoses, and translates into incredibly powerful lifting ability. King Hieron’s ship lifting challenge would present no difficulty to a modern hydraulic crane. Hydraulic cranes are capable of lifting anything from 42 tonnes upwards, meaning there are very few loads they cannot tackle in a ship loading or unloading situation. They are used to moving vast, heavily laden containers at speed and with extreme precision. The advent of container ships and the cranes used to load and unload, saw the decline of the traditional docker in harbours such as Liverpool Docks. Where it used to take hundreds of men to load and unload ships, container cranes that could do the job at the flick of a switch replaced the dockers, almost overnight.
Harbour cranes can be in a fixed position, or mobile. Mobile harbour cranes are useful in smaller harbours, as they can be positioned precisely for each load and any type of ship. More often, in large busy harbours, they are in a fixed position.
How Do Hydraulics Facilitate Lifting?
Simply put, hydraulics systems are able to use the forces present in a liquid under pressure. They work by transferring these forces via a series of pumps and pistons. Hydraulic cranes drive pistons that are capable of moving and lifting levers, which in turn lift enormous weights. The fluid is either a light oil, or water. Hydraulic hoses are high-pressure hoses that carry the fluid in order to transport the force. They can be made of thermoplastic, rubber, or be Teflon reinforced, depending on the type of fluid and the strength of the force being transmitted. Hydraulic hoses are often custom-made for specific jobs, but come in standard lengths, and sizes. They use custom-made connectors to connect to different types of machine. Custom Fittings will supply any type of connector, from NPT Fittings to stainless steel ORFS fittings.
Clearly, the maintenance of hydraulic hoses and the hydraulic fittings is essential for operator safety, since the pressure of the liquid within the hoses is extremely high. Leaks and breakages can be extremely hazardous. Operators are trained to spot damage to hoses, which must be inspected every day. Damage can occur due to stretching, crushing or twisting the hoses, which must be protected from sudden extremes at all times. Sudden rises or drops in temperatures can cause damage, as can rises and drops in the internal pressure. Using the wrong type of hose, or the wrong type of fitting can cause breakages too. Hydraulics are high maintenance, but with well trained operators, their benefits can far outweigh the difficulties they present.