Page 330 - 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

Ceramic disc tap heads are ‘handed’. In other words, there are specific hot tap
head workings, which turn to the left, and specific cold tap head workings,
which turn to the right, and they are usually colour coded for easy identification.
Ceramic disc taps are not universal. If replacement head workings are required
during maintenance operations, the correct type for the make of tap will be
needed.
p Figure 5.105 Ceramic discs
Shower mixer valves

Shower mixer valves mix water from both the cold water and hot water
installations, and discharge the mixed water from a showerhead. They can
be either:

● manual mixing valves
● venturi boost mixing valves
● pressure compensating mixing valves
● thermostatic mixing valves – for example:
● wax capsule type
● bi-metal coil type.

Shower valves are available in three styles:
1 exposed, surface-mounted valves – mounted on the surface, generally with
concealed pipework
2 concealed valves – all the valve and pipework is concealed with only the
controls on show
3 bar valves – a recent addition, an exposed-type shower valve designed to
be thin and modern looking.
Externally, all mixing valves appear very similar in style and most have common
distances of 150 mm between the hot and cold connections. The difference is in
the internal workings of the shower. In this part of the chapter, we will look at
those differences.
The requirement of all shower valves is that they blend hot and cold water to
the required temperature.

Manual mixing valves
Manual mixing valves do not have thermostatic control. They rely wholly on the
hot and cold supplies being balanced in terms of pressure and flow rate. Once
the temperature of the blended water has been adjusted, it remains fixed and
does not adjust to fluctuations in flow rate, pressure or temperature. For this
reason, the temperature of the hot water needs to be stable.
Although manual mixing valves can be used on high-pressure supplies, they are
best suited to low-pressure installations to avoid pressure fluctuations. They
should not be fitted to systems that contain instantaneous water heaters or
combination boilers.
Venturi boost mixing valves
The venturi mixing shower valve is specifically designed for installations that do
not have balanced hot and cold supplies, such as mains-fed cold water and

318

9781510416482.indb 318 29/03/19 8:59 PM