Page 318 - 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

DB pipe interrupters are generally used externally as attachments to hose
union bib taps and must not be used on appliances that have a control valve
restriction, such as a washing machine. They are resistant to frost damage. They
must be fitted vertically and have no valves fitted downstream of the device.
Some DB interrupters are manufactured with bayonet-type attachments for
domestic garden perforated hose irrigation systems.

Type EA and type EB verifiable and non-verifiable
single check valves

These two valves are the simplest of all mechanical backflow prevention devices
and can be used to protect against fluid category 2 for both back pressure and
back siphonage. Generally regarded as point-of-use protection, they consist of
a spring-loaded one-way valve that will allow water to flow from upstream to
downstream only. If back siphonage or back pressure occurs, the valve will shut
to prevent a reverse water flow. When no water is flowing, the valve remains in
the closed position. Both types are almost identical in appearance. The difference
between them is that the type EA device has a test nipple situated on the
upstream side of the valve so that it can be tested while in position to verify that
it is working correctly. The type EB non-verifiable single check valve does not have
a test point but can be used in the same way as the type EA single check valve.

Spring-loaded valve

Direction
of flow

Valve guide End on
view
Test point Stainless steel spring

Spring-loaded valve

Direction
of flow

Valve guide End on
Stainless steel spring view

Suitable for protection against fluid category:

Type EA/EB single check valve
2 Back 2 Back
pressure
siphonage
p Figure 5.81 Type EA verifiable single check valve and type EB non-verifiable single check valve

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