Page 516 - 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 filling loop is generally fitted to the return pipe close to the expansion
vessel and may even be supplied as part of the expansion vessel assembly.

Methods of releasing air from heating systems

When filling the system, air must be released to allow components such as heat
emitters to work properly. Air is released by several methods:
l The open vent (on vented systems) allows air to escape from the pipework
and the boiler as the system fills with water.
l Air release valves are sited on every heat emitter. These must be manually
opened with a suitable radiator air release key to enable the air to escape as
the system fills. Once water is detected, the air release valve is then closed.
l Automatic air release valves may be fitted in those places on the system where
air is expected to collect, such as high points in the pipework and the coil heat
exchanger on the cylinder. These were mentioned earlier in this chapter.
l Sealed systems must be filled, via the filling loop, taking care to avoid
over-pressurising the system. The boiler manufacturer’s recommendations
on filling, venting and final system pressure must be followed.

Selection of fuels for heat-producing
appliances

Types of fuels used for heat-producing appliances are:
l gas (both natural and LPG)
l oil
l solid fuel.

Gas
Natural gas is the most popular fuel for central heating in the UK. It comes from
a variety of sources, including the North Sea, the Middle East and Russia. It is a
naturally occurring gas that consists of a number of other flammable and inert
gases:
l methane
l ethane
l propane
l butane
l hydrogen
l carbon dioxide
l nitrogen.

Oil
Oil-fired appliances are popular where access to mains gas is difficult. They offer
a viable alternative to gas appliances. Most oil-fired appliances use C2 grade
28 second viscosity oil (kerosene), although other types of oil, such as heavy
heating oil, are available.

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