The velocity ratio of Weston’s differential pulley is :

(Where R : Radius of bigger pulley r : Radius of smaller pulley)

Concept:

Weston’s differential pulley:

• This uses an endless chain or rope wound over an upper pulley block, consisting of two pulleys of differing diameters, and a lower pulley block carrying the load, with a loop, where the effect is applied.
• During one revolution of the upper pulley wheels, the loop supporting the lower loop carrying the lower pulley-block will have its overall length altered by the difference between the amount wound off the smaller pulley, which π(D - d).
• This is shared by both lengths, So both the pulley block and the load will be divided and raised by 
• During this time the effort will move through a distance of the circumference of the large pulley πD.
• R : Radius of bigger pulley (D = 2R), r : Radius of smaller pulley (d = 2r)

Velocity ratio 

Velocity ratio 

Velocity ratio 

Velocity ratio 

Velocity ratio