Page 315 - 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

g HUK1 Hose union bib tap incorporating a double check 3 3
valve arrangement; permitted only as a replacement
for existing bib taps in house installations
h HC Diverter with automatic return (normally integral X 3
with some domestic appliance applications only)

Notes:
‘X’ indicates that the backflow prevention device is not acceptable for protection against back pressure
for any fluid category.
Arrangements incorporating a type DB device shall have no control valves on the outlet of the device.
The device shall not be fitted less than 300 mm above the spill-over level of an appliance and must
discharge vertically downwards.
Relief ports from BA and CA devices should terminate with an air gap, the dimension of which should
satisfy a type AA air gap.

Type BA verifiable backflow preventer with reduced
pressure zone (a reduced pressure zone valve)
Better known as an RPZ valve, this is a mechanical, verifiable, backflow prevention
device, offering protection to water supplies up to and including fluid category 4.
Verifiable simply means that the valve can be checked via test points to see if it is
working correctly (verified).

Valve open Valve open
Normal
direction
of flow
Normal direction of flow

Relief port Valve closed
Valve closed Valve open

Normal direction of flow
Direction
of
backflow

Type BA or reduced pressure zone valve
(RPZ valve). Valve open
Suitable for protection against fluid category: Relief port

Back Back
4 4
pressure siphonage
p Figure 5.76 An RPZ valve cut-away
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