Page 426 - 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

Expansion of hot water pipework

When the pipework of the hot water system is filled with hot water, the
heated pipework will expand. As the pipework cools down, it will contract. This
expansion and contraction must be accommodated for during the installation
process or noise within the installation will result. Pipes that pass through walls
and floors where not enough room has been left for expansion will ‘tick’ and
‘creak’ as the expansion and contraction takes place.
The rate of expansion will depend upon the material the pipe is made from.
It is known as the coefficient of linear expansion. Generally, pipework made
from plastic materials tends to expand more than that made from copper. The
coefficients of linear expansion for polybutylene and copper are as follows:
● the coefficient of linear expansion of plastic pipe is 0.00018 per metre per °C
● the coefficient of linear expansion of copper pipe is 0.000016 per metre per °C.
This means that, for every degree rise in temperature, polybutylene pipe will expand
0.00018 m in every metre and copper will expand 0.000016 m in every metre.
ACTIVITY

To calculate the amount of expansion that takes place on a given length of pipe:
Length of pipe (m) × coefficient of linear expansion × temperature rise
What is the expansion on a 15 mm copper pipe 6 m in length, when the pipe is
heated from 10°C to 60°C?
6 × 50 × 0.000016 = 0.0048 m or 4.8 mm
Now attempt these examples:
1 What is the expansion on a 15 mm polybutylene pipe 6 m in length, when
the pipe is heated from 10°C to 60°C?
2 What is the expansion on a 15 mm copper pipe 20 m in length, when the
pipe is heated from 15°C to 50°C?
3 What is the expansion on a 15 mm copper pipe 30 m in length, when the
pipe is heated from 12°C to 58°C?

Installation of shower mixing valves and shower
boosting pumps

In Chapter 5, Cold water systems, we looked at shower mixing valves and the various
types of shower boosting pumps. In the next section of this chapter we will take this
a step further and see how we install these appliances within hot water systems.

As we have already seen, there are a number of different shower valves available,
ranging from bath/shower mixer taps and simple shower mixing valves to
thermostatic and pressure balancing shower valves. The method of installation is,
in most cases, the same for each type of valve, with the requirement that equal
pressure and flow rate exist on both the hot water and cold water installations.
There are five methods of installation:

1 simple installations from a storage cistern in roof space supplying water to both
hot and cold water systems, thus ensuring equal pressures across both systems
2 installations that include an inlet, twin impeller shower-boosting pump
(often called a ‘power shower’)
414

9781510416482.indb 414 29/03/19 9:02 PM