Page 405 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 6 Hot water systems

l pressure reducing valves
● shock arrestors/mini expansion vessels.

Note: the eight specialist components listed above were covered in Chapter 5,
Cold water systems.
The controls for vented/unvented hot water storage systems fall into two
categories:
1 safety
2 functional.

In this part of the chapter, we will look at the various controls and components
for unvented hot water storage systems, their function and the position that
they occupy within the system.

Pressure
relief
valve Temperature
& pressure
reducing
valve
In-line
strainer

Tundish

Pressure
reducing
valve

Isolation valve
Single check valve

p Figure 6.40 The controls on a modern UHWSS

Safety controls

With the water inside the storage vessel at a pressure above atmospheric
pressure, the control of the water temperature becomes vitally important. This is
because, as the pressure of the water rises, so the boiling point of the water rises.
In simple terms, if total temperature control failure were to occur, the water
inside the vessel would eventually exceed 100°C, with disastrous consequences.
The graph in Figure 6.41 demonstrates the pressure/temperature relationship.

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