Page 370 - 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

The connections for the cold feed and draw-off are usually male thread
connections, while the primary flow and return connections have female
threads.
Hot water draw-off connection 1" male thread

Immersion heater connection

Primary flow connection
1" female thread
The direct water cylinder does not
contain any form of heat exchanger.
The water in the cylinder is the same
water that is in the boiler

Alternative primary flow connection
1" female thread. Position depends
on the manufacturer

Primary return connection
1" female thread

Cold feed connection
1" male thread

p Figure 6.2 Direct cylinder

The boiler can either be a small gas-fired hot water heater (often called a gas
circulator), designed to heat the water directly, or a small back boiler situated
behind a solid fuel fire. Because the water in the boiler comes direct from the
hot water storage cylinder, the boiler must be made of a material that does not
rust. This is to prevent rusty water being drawn off at the taps. Suitable boiler
materials are:

● copper
● stainless steel
● bronze.
The hot water circulates from the boiler or circulator by the principle of convection.
This is known as gravity circulation (see Chapter 3, Scientific principles). The hot
water rises in the primary flow pipe, directly heating the stored water in the
cylinder before the cooler water returns to the boiler. The water in the cylinder
does not heat uniformly. The water at the top of the cylinder is usually 10°C hotter
than at the bottom (generally 60°C at the top, 50°C at the bottom). This is known
as stratification and is desirable in stored hot water systems.

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