Page 320 - 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

Direction Spring-loaded valve
of flow

End on
Stainless steel spring Valve guide view
p Figure 5.83 Type ED non-verifiable double check valve

Type HA hose union backflow preventer (permitted
for use only on existing hose union bib taps in house
installations)
As the name suggests, this mechanical backflow prevention device screws onto
the outlet thread of a hose union bib tap. It is specifically for use with existing
hose union bib taps that do not have any form of backflow protection. It is
used to protect against back pressure at fluid category 2 and back siphonage at
fluid category 3.

Normal direction of flow

Connection to hose
union bib tap

Rubber membrane
Connection to hose

Normal direction of flow

Air entering the hose pipe
Stainless steel when the water pressure drops
spring

2 Back 3 Back
pressure
siphonage
p Figure 5.84 Type HA hose union backflow preventer

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