Differential pulley in collaboration with Richard and George Tangye. According to Richard Tangye's autobiography, the Weston differential pulley evolved from the Chinese windlass, with an endless chain replacing the finite length of rope. He claimed that many engineering firms conceded on the difficulty of efficiently disengaging the chain from the teeth as the pulleys turned, but his firm developed a "pitch" chain which solved the issue. Marketed as "Weston Differential Pulley Blocks with Patent Chain Guides", the pulley had good sales, namely, 3000 sets in 9 months. It was displayed in 5 sizes — from to — at the 1862 International Exhibition
Wire rope spooling technology its behaviour and affects lifespan. Fleet angle should be between 0.25° and 1.25°, depending on the rope construction. The fleet angle can be varied by moving the first sheave closer to or further away from the drum. If the sheave is too close to the drum, the fleet angle will be greater than 1.25°; if it is too far away, the fleet angle will be less than 0.25°. Sometimes it is not possible to achieve the optimum fleet angle. Where there is no space to rig a sheave the requisite distance from the drum, two additional spooling devices are available.