Page 321 - 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

Type HUK1 hose union bib tap incorporating a double
check valve arrangement

This hose union bib tap incorporates two single check valves, one situated
at the inlet to the tap and one at the outlet. A screw-type test point is also
included on the tap body. They are fitted in the same way as a normal HU
bib tap. However, they are not suitable for new installations and can only
be used as replacements where a hose union bib tap already exists. This is
simply because the Water Supply (Water Fittings) Regulations state that any
mechanical backflow prevention device should be fitted within the envelope
of the building to prevent damage by freezing. They are suitable as protection
against fluid category 3 for both back pressure and back siphonage.

Rising spindle

Packing gland

Head workings
Single check valve
Fixed jumper

Washer
Single check valve

Test point

Back Back
3 pressure 3 siphonage

p Figure 5.85 Type HUK1 hose union bib tap with double check valve arrangement

Type HC diverter with automatic return

This refers to a mechanical backflow prevention device used in bath/shower
combination tap assemblies, which automatically returns the bath outlet open
to atmosphere if a vacuum occurs at the inlet to the device.

The type HC diverter with automatic return is usually incorporated into the
design of an appliance or fitting. It is not a ‘stand alone’ fitting that can be added
to the installation. A good example of a type HC diverter would be a bath/
shower mixing valve with a diverter valve to operate the shower. While pressure
is maintained, the diverter valve remains open and the water is fed to the shower
hose. Should loss of pressure occur, the diverter valve closes and any excess water
in the shower hose returns to the bath through the open tap, thus preventing the
water from back-flowing down the cold supply pipe. They are suitable for fluid
category 3 to prevent back siphonage only.
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