Backflow Protection: FAQs


What form of backflow prevention should be installed as point of use backflow protection?

Schedule 2 paragraph 15 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in

Scotland require every plumbing system to incorporate protection against backflow, this is often referred to as point of use backflow protection.

To be accepted as providing adequate backflow protection the backflow device or arrangement installed typically should:

  • Firstly be approved by the Regulator or a relaxation to authorise its use granted
  • Secondly be rated equal to or higher than the highest contamination risk (fluid category) downstream for the type of backflow (back pressure or back siphonage) a system is likely to be exposed to.
  • Thirdly be of an appropriate quality and standard.

As some backflow prevention arrangements and devices have operational limitations you should always check with the local water undertaker to make sure they are suitable for the intended application.

Please note: if high risk contaminants are likely to be present in a plumbing system, because these represent a greater risk to health, in addition to any point of use protection the water undertaker can also require the installation of zone or wholesite backflow protection.


Regulators Specification: Non-mechanical backflow protection 

Type

Description

Suitability by fluid category 

Back pressure 

Back siphonage 

AA

Air gap with unrestricted discharge above spillover level

5

5

AB

Air gap with weir overflow

5

5

AC

Air gap with vented submerged inlet

3

3

AD

Air gap with injector 

5

5

AF

Air gap with circular overflow

4

4

AG

Air gap with minimum size circular overflow determined by measure or vacuum test

3

3

AUK1

Air gap with interposed cistern 

3

5

AUK2

Air gaps for taps and combination fittings (tap gaps) discharging over domestic sanitary appliances, such as a washbasin, bidet, bath or shower tray shall not be less than the following: 

Size of tap or combination fitting

.
Not exceeding G ½
Exceeding G½ but not exceeding G ¾
Exceeding G ¾

 

Vertical distance bottom of tap outlet above spillover level of recieving appliance

20 mm
25 mm
70 mm

 

X

3

AUK3

Air gaps for taps or combination fittings (tap gaps) discharging over any higher risk domestic sanitary appliances where a fluid category 4 or 5 is present, such as:

  1. any domestic or non-domestic sink or other appliance; or
  1. any appliances in premises where a higher level of protection is required, such as some appliances in hospitals or other health care premises

Shall be not less than 20 mm or twice the diameter of the inlet pipe to the fitting, whichever is the greater

X

5

DC 

Pipe interrupter with permanent atmospheric vent

X

5

Notes:

  1. X Indicates that the backflow prevention arrangement or device is not applicable or not acceptable for protection against backpressure for any fluid category within water installations in the UK.
  2. Arrangements incorporating Type DC devices shall have no control valves on the outlet of the device; they shall be fitted not less than 300 mm (150 mm in Scotland) above the spillover level of a WC pan, or 150 mm above the sparge pipe outlet of a urinal, and discharge vertically downwards 
  3. Overflows and warning pipes shall discharge through, or terminate with, an air gap, the dimension of which should satisfy a Type AA air gap.


Regulators Specification: Mechanical backflow protection 

Type

Description

Suitability by fluid category 

Back pressure 

Back siphonage 

BA

Verifiable backflow preventer with reduced pressure zone

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

DUK1

Anti-vacuum valve combined with a 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

Divertor with automatic return (normally integral with some domestic appliance applications).

X

3

HUK1

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 combined with a check valve downstream

2

3

Notes:

  1. X Indicates that the backflow prevention arrangement or device is not applicable or not acceptable for protection against backpressure for any fluid category within water installations in the UK.
  2. Arrangements incorporating a Type DB 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 DUK1 shall have no control valves on the outlet of the device and be fitted on a 300 mm minimum Type A upstand.
  4. Relief outlet ports from Types BA and CA backflow prevention devices shall terminate with an air gap, the dimension of which should satisfy a Type AA air gap.

 


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Disclaimer

Uncontrolled if downloaded. This is informative, non-statutory guidance and intended for general guidance purposes only; it is subject to change.

Compliance with this information should not be relied upon as guaranteeing no enforcement action will be taken by water undertakers. Water Regs UK accepts no liability for loss, indirect or consequential loss arising from or in connection with this guidance document.


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