A hydraulic jigger is a hydraulically-powered mechanical

winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension (physics), tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a Bobb ...

. From the mid-19th century, hydraulic power became available throughout the increasingly modern dockyards and warehouses. This was generated centrally and distributed by pipework, either around a dock estate, or across a city by the new

hydraulic power network A hydraulic power network is a system of interconnected Pipe (fluid conveyance), pipes carrying pressurized liquid used to transmit Power (physics), mechanical power from a power source, like a pump, to hydraulic equipment like lifts or Hydrauli ...

s. The jigger was developed by William Armstrong, around 1840, as part of his hydraulic crane The hydraulic crane was the invention that first made his fortune and established the engineering and armaments firm of Armstrongs of Elswick. Armstrong's original invention of the jigger has been questioned, but he was the first to make widespread use of it.

Operation

The jigger was one of the first hydraulic machines of the Victorian age, after

Bramah Bramah is a surname. Notable people with the surname include: * Ernest Bramah (1868–1942), English author * John Joseph Bramah (1798–1846), English ironmaster and engineer * Joseph Bramah (1748–1814), English ironmaster and inventor, uncle o ...

hydraulic press A hydraulic press is a machine press using a hydraulic cylinder to generate a compressive force. It uses the hydraulic equivalent of a mechanical lever, and was also known as a Bramah press after the inventor, Joseph Bramah, of England. He inven ...

but before the continuously-rotating

hydraulic motor A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadly, ...

. It allowed the mechanism of the ram to be used to move over a usefully long distance, not merely the length of the ram. A jigger works like a pulley block, but in reverse. Rather than turning an easy pull on a rope into a powerful lift, the jigger uses the powerful force of a hydraulic ram, but limited in how far it can travel, to pull a long length of chain. The chain is looped several times lengthwise around the ram cylinder, running over a number of pulleys at each end. When the cylinder moves, the pull on the end of the chain is multiplied by the number of loops. The ''force'' of the jigger's pull is reduced similarly, according to how many times the chain was looped. As the cylinder had adequate power to begin with, and could simply be made larger in diameter when needed, this was not a significant limit on the jigger's force. Unlike cylinders, jiggers always provided a tension pull, rather than a compressive push. The first jiggers pre-dated the development of flexible steel

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and so they used wrought iron chain, rather than the natural fibre rope otherwise available. Later machines did switch to wire rope.

Concentric cylinders

Some applications, such as cranes, needed to lift both heavy and light (empty hook) weights. Loaded, heavy, lifts were made by the conventional cylinder, its diameter sized according to the maximum capacity. However even a light load on such a piston would still consume the same quantity of high-pressure water, which was charged for by consumption. To reduce this effect, compound pistons were used: two concentric pistons. When unloaded, the smaller central piston would move first. Only if this was held down by the load, the larger outer piston would also begin to move, lifting both pistons and the full load together.

Applications

The basic jigger mechanism was used very widely, for a range of machines across dockyards, warehouses, railway yards and engineering workshops. They were even to be found in theatres, lifting the stage curtains.

Cranes

The first application of jiggers had been for Armstrong's first hydraulic crane and this remained an important application for them. A distinctive type of crane was the warehouse wall crane or 'whip'. The ram was mounted vertically on an outside wall with a small jib or fixed pulley above it. The space available by external mounting allowed the use of long cylinders and very long lifts, spanning several floors.

Portable winches

Many dockyards used small portable jiggers mounted on wheeled carriages. These could be moved around the quays as needed, and plumbed into outlets in the hydraulic mains with screwed pipe unions. They were used as portable

es for all manner of tasks. A typical task would be winching bales out of the hold of a ship, up a sloping gangway. Bales of bulk products such as

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were made too large and heavy for dockers to lift by hand, and the jigger appeared at a time when cranes were still only in limited numbers.

Lifts

Jiggers were also used for freight lifts in warehouses and factories. These were not accepted for passenger carrying though, until 1854 and

Elisha Otis Elisha Graves Otis (August 3, 1811 – April 8, 1861) was an American industrialist and founder of the Otis Elevator Company. In 1853, he invented a safety device that prevents elevators from falling if the hoisting cable fails. On March 23, 18 ...

' invention of the safety brake, to prevent the carriage falling if the hoisting cable were to break.

Catapult launch

British

aircraft carrier An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a full-length flight deck and hangar facilities for supporting, arming, deploying and recovering carrier-based aircraft, shipborne aircraft. Typically it is the ...

s of World War II used a form of pneumatic-hydraulic jigger to power their

aircraft catapult An aircraft catapult is a device used to help fixed-wing aircraft gain enough airspeed and lift for takeoff from a limited distance, typically from the deck of a ship. They are usually used on aircraft carrier flight decks as a form of assist ...

s. The catapults had a travel and an 8:1 pulley ratio, requiring a power cylinder. One side of the cylinder was connected to a manifold of a dozen high-pressure compressed air bottles. Power for launching was supplied by the compressed air. The other side was filled with hydraulic fluid. When the launch valve was triggered, the hydraulic fluid pressure dropped rapidly as fluid was vented into an unpressurised catch tank. The piston was forced rapidly from the air end to the hydraulic end, pulling the crosshead and the jigger pulleys and drawing the launch trolley forwards. The average acceleration for an aircraft was 1 g, with a peak of 2.5 g. After launching, the piston was decelerated within the cylinder by a conical protrusion entering a narrow choke ring, and the hydraulic resistance increasing as the flow area reduced. Hydraulic fluid was then pumped from the catch tank by an electric pump and back into the cylinder under pressure. The cylinder was double-ended, with a piston rod and jigger at each end, and the catapult was retracted by the hydraulic pressure forcing the piston backwards, and re-compressing the air reservoirs.

References

{{Hydraulics Jigger Winches