Chapter 11 : Simple Lifting Machines 193
11.6.GEARED PULLEY BLOCK
It is an improved form of a differential pulley block in which the velocity ratio is intensified
with the help of gears. A geared pulley block consists of a cogwheel
A, around which is passed an endless chain. A smaller gear wheel
B, known as pinion, is keyed to the same shaft as that of A.
The wheel axle B is geared with another bigger wheel C,
called the spur wheel. A cogwheel D is keyed to the same shaft as
that of spur wheel C.
The load is attached to a chain, that passes over the cogwheel
D. The effort is applied to the endless chain, which passes over the
wheel A as shown in Fig. 11.4.
Let T 1 = No. of cogs on wheel A
(known as effort wheel),
T 2 = No. of teeth on wheel B
(known as pinion),
T 3 = No. of teeth on the wheel C.
known as spur wheel, and
T 4 = No. of cogs on the wheel D
known as load wheel.
We know that distance moved by the effort in one revolution of the cogwheel A,
=T 1 ...(i)
and no. of revolution made by the pinion B
=1
∴ No. of revolutions made by the spur wheel C
2
3T
T=and no. of revolutions made by the load wheel D
2
3T
T=∴ Distance moved by the load
2
4
3T
T
T=× ...(ii)and
Distance moved by the effort
V.R.
Distance moved by the load=^113(^224)
4
3
TTT
T TT
T
T
==×
×
...(iii)
Now M.A.
W
P
= ...as usual
and efficiency,
M.A
V.R.
η= ...as usual
Example 11.8. A geared pulley block, used to lift a load, has the following dimensions:
No. of cogs on the effort wheel = 90
No. of cogs on the load wheel = 8
No. of teeth on the pinion = 25
No. of teeth on the spur wheel = 40
Find the maximum load that can be lifted by an effort of 50 N on machine. Take efficiency of
the pulley block as 75%.
Fig. 11.4. Geared pulley block.