Page 192 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

100 kg lifting force 50 kg lifting force 25 kg lifting force

100 kg load 100 kg load 100 kg load

p Figure 3.27 Single pulley system p Figure 3.28 Two pulley system p Figure 3.29 Four pulley system

If four wheels are used and held together by a long rope or chain that loops over
them, the 100 kg weight is now supported by four ropes, which means that each
rope is supporting a quarter of the total 100 kg weight, or 25 kg. This means
that only a quarter of the force (25 kg) is needed to lift the weight (100 kg). This
system is known as a block and tackle.

Screws

In terms of simple machines, a screw is a machine that converts rotation into
a straight-line motion that can be placed vertically, horizontally or at an angle.
It is basically a cylinder or wedge with an incline plane wrapped around it.
It was originally designed as a simple water pump (the Archimedes screw), a
task for which it is still used today. It can be found in many objects, such as
screw fixings, bolts and threads on pipe. It can also be seen on drills and auger
bits, and as a means of moving solid fuel, such as coal, towards a boiler by its
rotary motion.

p Figure 3.30 The Archimedes screw IMPROVE YOUR MATHS
The following formula is used to calculate the mechanical advantage of a screw:

π × D
MA =
L
Where:
MA = mechanical advantage
π = 3.142
D = diameter
p Figure 3.31 The Archimedes L = length
screw in action as a water lifter

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