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Backflow Prevention Devices

Backflow Prevention

The simplest and most effective backflow preventer would be an air gap between any device that opens to a plumbing system, However with a submerged mains inflow a backflow preventer is required to protect the potable water from contamination hazards.

There are many different causes for backflow some of the main reasons are:

  • A sudden drop in water pressure
  • High demand for water in your street
  • Frozen pipework
  • Burst water mains

A backflow preventer is essential in the protection against contamination, these can be found in many forms and should be fitted in accordance with the current guidelines and regulations as these are required by law in certain applications.

There are over 10,000 recorded cases of backflow contamination each year (some being fatal) which indicates the importance of a backflow prevention device.

Most backflow preventers will incorporate test points and isolation valves which allow for annual inspection and maintenance.


Schedule of mechanical backflow prevention arrangements

 

 

 

Suitable for protection

against fluid category

Type

Description of Backflow Prevention arrangements and devices

Back-Pressure

Back-Siphonage

AA

Unrestricted air gap

5

5

BA

Verifiable backflow preventer with reduced pressure zones

4

4

CA

Non-verifiable disconnector with difference between pressure zones not greater than 10%

3

3

DA

Anti-vacuum valve (or vacuum breaker)

X

3

DB

Pipe interrupter with atmospheric vent and moving element

X

4

DC

Pipe interrupter with permanent atmospheric vent

X

5

DUKI

Anti-vacuum valve combined with single check valve

2

3

EA

Verifiable single check valve

2

2

EB

Non-verifiable single check valve

2

2

EC

Verifiable double check valve

3

3

ED

Non-verifiable double check valve

3

3

HA

Hose union backflow preventer. Only permitted for use on existing hose union taps in house installations

2

3

HC

Diverter with automatic return (Normally integral with some domestic appliance applications only)

X

3

HUKI

Hose union tap which incorporates a double check Valve. Only permitted for replacement of existing hose union taps in house installations.

3

3

LA

Pressurised air inlet valve

X

2

LB

Pressurised air inlet valve with a check valve downstream

2

3

 

 

Notes:

1.       X indicates that the backflow prevention device is not acceptable for protection against backflow for any fluid category within water installations in the UK.

2.       Arrangements incorporating a Type DB backflow prevention device shall have no control valves on the outlet of the device. The device shall be fitted not less than 300mm above the spillover level of an appliance and discharge vertically downwards.

3.       Types DA and DUKI backflow prevention devices chall have no control valves on the outlet of the device and be fitted on a 300mm minimum Type A upstand.

4.       Relief Outlets from Type BA and CA backflow prevention devices shall terminate with an air gap, the dimension of which should satisfy a Type AA air gap.

 
 
Advanced Water Company
Unit D5 Enterprise Centre
Off Enterprise Way
Vale Park, Evesham
Worcestershire. WR11 1GS