Page 494 - 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

Black water at the
air release valve
when the system
is bled

Sludge blocks
boiler heat The sludge is
exchangers, attracted to
causing noise circulators

The problems
of sludging
Sludge blocks
Sludge leads to
the formation of pipework, preventing
the heat getting to
hydrogen gas
the radiators

The sludge sits at
the bottom of
radiators, creating
cold spots

p Figure 7.54 The problems of sludging

Corrosion inhibitor:
l stops a build-up of ‘black oxide sludge’, the major cause of central heating
problems
l helps to reduce fuel costs
l helps prevent the formation of hydrogen gas
l has a non-acidic neutral formation and so is harmless to the environment
l prevents pin-holing of radiators and pipework
l prevents scale formation.
It should be remembered that corrosion inhibitor must not be added to systems
that contain a single feed self-venting cylinder as these use air entrapment to
separate the primary and secondary systems. Should the air bubbles within
the cylinder break, this would lead to the inhibitor chemicals mixing with the
domestic hot water supply, causing contamination.

The use of magnetic filters

As we have already seen, black oxide sludge is made up of minute particles of
steel that have been ‘robbed’ by electrolytic corrosion and this is attracted to
components such as circulating pumps, causing pump failure and damage to
the system.

Magnetic filters protect central heating systems by using very powerful magnets
to attract the suspended black oxide steel particles in the central heating
system water. This can remove almost 100 per cent of suspended particles,
p Figure 7.55 A magnetic filter preventing further build-up of black oxide sludge.

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