Page 400 - 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

Secondary circulation is a method of returning the hot water draw-off back to
INDUSTRY TIP the storage cylinder in a continuous loop, to eliminate cold water ‘dead legs’ by
reducing the distance the hot water must travel before it arrives at the taps.
A secondary circulation pump
is very similar in design to In all installations, secondary circulation must use forced circulation via a
a central heating circulator. bronze- or stainless steel-bodied circulating pump to circulate the water to and
The difference is that the from the storage cylinder. The position of the pump will depend on the type of
secondary circulating pump hot water system installed.
has a body cast from bronze
to eliminate discoloured water Secondary circulation installations on unvented hot
and subsequent contamination. water storage systems
Bronze, as we discovered in
Chapter 3, is a non-ferrous In most cases, a secondary circulation connection is not fitted on an unvented
metal that does not rust. Central hot water storage vessel and, unlike open vented hot water storage vessels,
heating circulators have a cast it is not possible to install a connection on the vessel itself. Where secondary
iron or steel body that would circulation is required, this must be taken to the cold water feed connection
rust if used on a secondary using a swept tee just before the cold feed enters the unit. To safeguard against
circulation system. Under no reverse circulation, a non-return valve or single check valve must be fitted after
circumstances should a central the circulating pump and just before the swept tee branch. The pump should be
heating circulator be used. fitted on the secondary return, close to the hot water storage vessel.

Isolation valve

In-line strainer

Pressure reducing valve
Balanced cold
connection

Single check
valve Pressure
relief valve
Expansion bubble
Temperature
relief valve
Tundish

Single check
valve

Swept
'tee'
Bronze pump
Secondary circulation

p Figure 6.35 Secondary circulation on an unvented hot water storage installation

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