POWERHOUSE COLLECTION

Differential pulley block made by Tangyes Ltd

Object No. 2003/45/1

T.A. Weston's differential pulley has significance in regard to the development of ideas on the nature of lifting devices, collaborative practices between Weston the innovator and Richard, George, and James Tangye (who were brothers in a leading family of nineteenth-century English industrialists), and the display of the product at the 1862 International Exhibition in London. The product was also the subject of a controversial patent infringement claim, which involved disputes about priority and novelty. Weston's differential pulley (disparagingly referred to as 'the poor man's chain hoist') became the standard for the design and manufacture of simple lifting devices. This was partly achieved by switching from the use of materials; from using an endless rope to an endless chain for the purpose of mechanical advantage in lifting weights, and partly through the collaboration between Weston and Sir Richard Tangye (1833-1906) and his brother George, who were leading nineteenth-century industrialists and who were the only firm of English engineers to manufacture this pulley. In the history of technology the Weston differential pulley was, according to Richard Tangye's 1889 autobiography, evolved from the ancient Chinese windlass. The windlass utilises two small drums or barrels, a crank handle, and a single small pulley to raise a weight, rather than two sheaves and an endless chain. Weston was familiar with the operation of the Chinese windlass, and first used this apparatus to raise a boat that had sunk off the port of Boston (USA). The windlass was a standard one, in that it consists of a barrel, one half of which was smaller in diameter than the other half. Rope ends are wound around (in an opposite direction) each section of the barrel, leaving a loop in the middle which carries a pulley block. Each revolution of the barrel winds on the large diameter section, a length of rope equal to the large circumference. At the same time, the rope on the smaller section of the barrel is unwound to a length equal to the circumference of the smaller section of the barrel. Consequently, the weight is lifted through a height equal to half the difference in circumference of the two ends of the barrel. Weston changed this set-up slightly. He retained the windlass, but substituted an endless rope for the rope ends that were attached to the differential barrel. The significance of this was that the end rope gave a mechanical advantage for the weight lifted, in that a substantially reduced length of rope could now be used to lift the same weight. Another significance may be ascribed to Weston's change in material for the pulling device of the pulley; from rope to an iron chain. Weston had found that rope slippage was a disadvantage. He changed to iron chain and had it 'gear' into teeth in the face of the barrel. The Weston differential pulley was thus 'born' and has changed little from Weston's innovative work in the second-half of the nineteenth century. In his autobiography (1889), Sir Richard Tangye claimed that many mechanical engineering firms turned away from the challenge of making Weston's differential pulley. Tangye considered the central difficulty was in designing a tooth or projection (1889, 70) in the grooves of the pulley. The chain had to be quickly and cleanly disengaged from the teeth as the pulleys revolved. Weston approached Tangyes after other engineering firms declined to make his diffential pulley. Initially, Richard and George Tangye also experienced difficulties in manufacturing the pulley to Weston's specifications. After a few months away trying to improve his ideas, Weston returned to Tangyes and began a more fruitful collaboration with Richard and George. On the second occasion, Tangyes directed their attention to the nature of the chain, and it was decided that a pitch chain be made to solve the problems that were being encountered with the pulley. Tangyes' development of the pitch chain was a significant breakthrough in the development of Weston's differential pulley. A pitch chain is one where the links are the same in size and shape. According to Richard Tangye (1889, 72), British chainmakers were incapable of making pitch chain, and interestingly, once Tangyes produced the chain, they received high praise from the Block Chain Makers Association and the Midland Counties Trades Federation (see the product advertisement entitled, Weston Differential Pulley Blocks with Patent Chain Guides, enclosed). Another important breakthrough for Tangyes was that they were able to successfully forge the final link to close the chain. The issue of patent infringement concerned issues of priority and novelty of invention. An unmamed ironmonger from Bristol, who "was backed up by some rich people" (Tangye, 1889, 74), challenged Tangyes in court over their claimed originality of the differential pulley. The ironmonger claimed that the pulley had been in use for thirty years prior to Weston's patent. This was a serious claim, and had it been established, then the reputation of both Weston and Tangye would most likely have been damaged. Fortunately for both men, the model of the differential pulley that was presented as evidence in court was significantly different from the Weston in that it relied upon the chain "falling upon a series of spikes in the periphery of the pulley"(1889, 75), whereas in Weston's block, the periphery of the pulley was divided into a series of beds for the reception of the links. Despite the appellant's case for restitution, which involved evidence from the blockmaker, the chainmaker, the salesman, and the manufacture, the case was found in favour of the defendant, with the judge, Sir William Page Wood declaring: "as in the case of every other mechanical invention, the principle had long been known, yet the plaintiff (Mr Weston), as the man who had for the first time given life to that principle, and produced an invention in such a perfected state that mankind could avail themselves of it, was entitled to be protected in the enjoyment of his patent" (1889, 84-85). Once in production (about 1862), the differential pulley sold well, in fact, demand increased substantially. Tangyes exhibited the pulley (five different sizes) at the 1862 International Exhibition (London). The sizes of the pulley varied from 10 cwt (508 kilograms) to 3 tons (3.04 tonnes). In the exhibition, the Weston differential was classified in Class V111 (Machinery in General), and was assigned no. 2020. The pulley was awarded a medal, with the judge's commenting: "Original application, practical utility and success" (Report, 1863, Class V111, 20). Tangyes sold about 3,000 sets of pulleys in nine months. The Weston differential pulley eventually became a standard for this type of lifting device. References International Exhibition 1862. (1863). Reports by the Juries on the Subjects in the Thirty-Six Classes into which the Exhibition was Divided. William Clowes and Sons, London. Parker, J.F. (1920/21). 'Some Notes on the Tangye Family', Transaction of the Newcomen Society, Vol. 45, 191-205. Tangye, R. (1889) (4th ed.). One and All: An Autobiography of Sir Richard Tangye of the Cornawall Works, Birmingham. S.W. Partridge and Co., London. Waterhouse, R. E. (1957). A Hundred Years of Engineering Craftsmanship: A Short History Tracing the Adventurous Development of Tangyes Limited, Smethwick, (1857-1957). Tangyes Limited, London.