Page 319 - 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 5 Cold water systems

Both valves are manufactured from DZR resistant brass and have either type A
compression fittings or female BSP threads for connection to the pipework. The
valves should conform to BS 6282 Part 1 for use in hot or cold water systems
up to 90°C.
In domestic premises the risk from fluid category 2 generally occurs where the
hot and cold supplies are taken to a single terminal fitting such as mixer taps
or shower valves. This is known as a cross-connection. However, care must be
taken when installing single check valves to hot water supplies as the expansion
of the water can cause excessive pressure on the check valve causing it to fail.
Other uses include the cold water connections to drinks machines.

Type EC and type ED verifiable and non-verifiable
double check valves
These are mechanical backflow prevention devices consisting of two single
check valves in series, which will permit water to flow from upstream to
downstream, but not in the reverse direction. They are used primarily to protect
against fluid category 3 for both back pressure and back siphonage.
The type EC verifiable double check valve has two test nipples, one on the
upstream side of the first check valve and another in the chamber between the
first and second check valves. These are used to verify that the valve is working
correctly. The type ED non-verifiable double check valve does not have a test
point but can be used in the same way as the type EA single check valve.

Suitable for protection against fluid category:
Type EC/ED double check valves

3 Back 3 Back
siphonage
pressure
Direction Spring-loaded valve
of flow

End on
view
Test point Test point Valve guide
Stainless steel spring
p Figure 5.82 Type EC verifiable double check valve

Typical uses in domestic installations include garden hose union bib taps and
sealed heating systems fitted in conjunction with a temporary filling loop.
When used with sealed heating systems, the double check valve must be fitted
to the cold water supply connection to the filling loop and not to the sealed
heating connection.

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