Page 190 - 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

l Length of the pipe: flow rate diminishes with length because of the frictional
resistance of the wall of the pipe. Water flows faster down the centre of
the pipe than it does at the pipe wall. The nearer the water is to the wall
of the pipe, then the greater the frictional resistance and so the slower the
water becomes. The frictional resistance of the pipe is slowing the flow rate
constantly. The greater the length, the more frictional resistance, the greater
the loss of flow rate. To counter this effect, the pipe size should be increased
initially at the start of the pipe run and then reduced as length increases.
l Frictional resistance of the internal bore of the pipe: different materials
offer different frictional resistance. Polybutylene pipe, for instance, has the
smoothest bore of all common pipe materials and low carbon steel the
roughest. Therefore, low carbon steel at like-for-like sizes will have a much
lower flow rate than polybutylene pipe.
l Constrictions such as valves and taps: taps and valves offer a lot of
resistance to the flow of water. Some stop taps can increase pipe length by
up to 6 m per valve.

5 THE MECHANICAL PRINCIPLES

IN THE PLUMBING AND HEATING

INDUSTRY

Simple machines are those that aid with the lifting and moving of loads that are
too heavy to lift or move on their own. There are four main types:

1 levers
2 wheel and axles
3 pulleys
4 screws.
IMPROVE YOUR These machines give a mechanical advantage (velocity ratio) to human effort,
MATHS meaning they multiply the force that is put into them. There are two types of
The calculation for finding out mechanical advantage:
how a lever functions is:
1 Ideal mechanical advantage (IMA): purely theoretical, based upon an
Load
Mechanical advantage = ‘ideal machine’, which does not exist.
Effort
2 Actual mechanical advantage (AMA): this is the mechanical advantage
of a real machine such as a wheelbarrow (lever). AMA takes into
consideration real-world factors such as energy lost because of friction.

Simple machines

Here, we will look at the machines themselves and their possible uses in
everyday working life.

Levers
In physics, a lever is a rigid object that can be used with a pivot point or fulcrum
to multiply the mechanical force that can be applied to another, heavier object.
Levers are examples of mechanical advantage.

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