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Backflow and Back-Siphonage Prevention Device Regulations

Backflow and Back-Siphonage Prevention Device Regulations

The following links are specifications and definitions of diffrent types of backflow prevention devices, including air gaps, pipe interrupters and Reduced Pressure Zone Valves (RPZ).

Links to entries below:


1. Air Gaps

An air gap means a visible, unobstructed and complete physical air break between the lowest level of water discharge and the level of potentially contaminated fluid downstream (critical water level) within a cistern, vessel, fitting or appliance, hereinafter called a receptacle, that:
  • is not less than 20 mm or twice the internal diameter of the inlet pipe whichever is the greater; and
  • from which water discharges at not more than 15° from the vertical centreline of the water stream.

 

1.1 Type AA - Air Gap with Unrestricted Discharge

A non-mechanical backflow prevention arrangement of water fittings where water is discharged through an air gap into a receptacle which has, at all times, an unrestricted spillover to atmosphere.

Maximum permissible fluid category against which a Type AA air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 5
  • Backflow by back siphonage: Fluid Category 5

 

1.2 Type AB - Air Gap with Weir Overflow

A non-mechanical backflow prevention arrangement of water fittings complying with Type AA, except that the air gap is the vertical distance from the lowest point of the discharge orifice which discharges into the receptacle, to the critical water level of the rectangular weir overflow.

Maximum permissible fluid category against which a Type AB air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 5
  • Backflow by back siphonage: Fluid Category 5
Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.

 

1.3 Type AC - Air Gap with Vented Submerged Inlet and Circular Overflow

A non-mechanical backflow prevention arrangement of water fittings with a vented, but submerged, inlet; the air gap being measured vertically downwards from the lowest point of the air inlet to the critical level.

Maximum permissible fluid category against which a Type AC air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 3
Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.

 

1.4 Type AD - Air Gap with Injector

A non-mechanical backflow prevention arrangement of water fittings with a horizontal injector and a physical air gap of 20 millimetres or twice the inlet diameter, whichever is the greater.

Maximum permissible fluid category against which a Type AD air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 5
  • Backflow by back siphonage: Fluid Category 5

 

1.5 Type AF - Air Gap with Circular Overflow

A non-mechanical backflow prevention arrangement of water fittings with an air gap measured downwards from the lowest point of the discharge orifice, which discharges into the receptacle, to the critical level.

Maximum permissible fluid category against which a Type AF air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 4
  • Backflow by back siphonage: Fluid Category 4
Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.

 

1.6 Type AG - Air Gap Arrangement with Minimum Size Circular Overflow

A non-mechanical backflow prevention arrangement of water fittings with an air gap; together with an overflow, the size of which is determined by measure or a vacuum test.

Maximum permissible fluid category against which a Type AG air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 3
Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.

 

1.7 Type AUK1 - Air Gap with Interposed Cistern

A non-mechanical backflow prevention arrangement consisting of a cistern with a Type AG overflow and an air gap; the spill-over level of the receiving vessel (WC pan or other receptacle) being located not less than 300 millimetres below the overflow pipe and not less than 15 millimetres below the lowest level of the interposed cistern.

Maximum permissible fluid category against which a Type AUK1 air gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 5
Note: overflow and warning pipes shall discharge through or terminate with an air break, the dimensions of which should satisfy a Type AA air gap.

 

1.8 Type AUK2 - Domestic Tap Gap

The height of air gap between the lowest part of the outlet of a tap, combination fitting, shower head or other fitting discharging over a domestic sanitary appliance or other receptacle, and the spillover level of that appliance, where a fluid category 2 or 3 risk is present downstream.

Maximum permissible fluid category against which a Type AUK2 tap gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 3

 

1.9 Type AUK3 - Higher Risk Tap Gap

The height of an air gap between the lowest part of the outlet of a tap, combination fitting, shower head or other fitting discharging over any appliance or other receptacle, and the spillover level of that appliance, where a fluid category 4 or 5 risk is present downstream.

Maximum permissible fluid category against which a Type AUK3 tap gap is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 5

 

 

2. Pipe Interrupter

 

2.1 Type DC Pipe Interrupter

A non-mechanical backflow prevention device with a permanent unrestricted air inlet, the device being installed so that the flow of water is in a vertical downward direction.

Maximum permissible fluid category against which a Type DC arrangement is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 5
Note: arrangements incorporating Type DC devices shall have no control valves on the outlet of the device, they shall be fitted not less than 300mm above the spillover level of a WC pan, or 150mm above the sparge pipe outlet of a urinal, and discharge vertically downwards.

 

 

3. Backflow Prevention Devices

 

3.1 Type BA – Verifiable backflow preventer with reduced pressure zone

A verifiable mechanical backflow prevention device consisting of an arrangement of water fittings with three pressure zones with differential obturators and that will operate when potential backflow conditions obtain or there is a malfunction of the valve.

Maximum permissible fluid category against which a Type BA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 4
  • Backflow by back siphonage: Fluid Category 4
Note: relief ports from Type BA backflow prevention devices shall terminate with an air gap, the dimension of which should satisfy a Type AA air gap.

 

3.2 Type CA – Non-verifiable disconnector with different pressure zones

A non-verifiable mechanical backflow prevention device which provides disconnection by venting the intermediate pressure zone of the device to the atmosphere when the difference of pressure between the intermediate zone and the upstream zone is not greater than 10% of the upstream pressure.

Maximum permissible fluid category against which a Type CA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 3
Note: relief ports from Type CA backflow prevention devices shall terminate with an air gap, the dimension of which should satisfy a Type AA air gap.

 

3.3 Type DA – Anti-vacuum valve (or vacuum breaker)

A mechanical backflow prevention device with an air inlet which is closed when water within the device is at or above atmospheric pressure but which opens to admit air if a vacuum occurs at the inlet to the device.

Maximum permissible fluid category against which a Type DA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 3

 

3.4 Type DB – Pipe interrupter with atmospheric vent and moving element

A mechanical backflow prevention device with an air inlet closed by a moving element when the device is in normal use but which opens and admits air if the water pressure upstream of the device falls to atmospheric pressure, the device being installed so that the flow of water is in a vertical, downward direction.

Maximum permissible fluid category against which a Type DB device is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 4

 

3.5 Type DUK1 – Anti-vacuum valve combined with a single check valve

A mechanical backflow prevention device comprising an anti-vacuum valve with a single check valve located upstream.

Maximum permissible fluid category against which a Type DUK1 device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 2
  • Backflow by back siphonage: Fluid Category 3
Note: Type DUK1 device shall have no control valves on the outlet of the device and be fitted on a 300mm minimum Type A upstand.

 

3.6 Type EA – Verifiable single check valve

A verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction.

Maximum permissible fluid category against which a Type EA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 2
  • Backflow by back siphonage: Fluid Category 2

 

3.7 Type EB – Non-verifiable single check valve

A non-verifiable mechanical backflow prevention device which will permit water to flow from upstream to downstream but not in the reverse direction.

Maximum permissible fluid category against which a Type EB device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 2
  • Backflow by back siphonage: Fluid Category 2

 

3.8 Type EC – Verifiable double check valve

A verifiable mechanical backflow prevention device consisting of two verifiable single check valves in series, which will permit water to flow from upstream to downstream but not in the reverse direction.

Maximum permissible fluid category against which a Type EC device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 3

 

3.9 Type ED – Non-verifiable double check valve

A non-verifiable mechanical backflow prevention device consisting of two single check valves in series, which will permit water to flow from upstream to downstream but not in the reverse direction.

Maximum permissible fluid category against which a Type ED device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 3
  • Backflow by back siphonage: Fluid Category 3

 

3.10 Type HA – Hose union back flow preventer

A mechanical backflow prevention device for fitting to the outlet of a hose union tap and consisting of a single check valve with air inlets that open if the flow of water ceases.

Maximum permissible fluid category against which a Type HA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid category 2
  • Backflow by back siphonage: Fluid category 3

 

3.11 Type HC – Diverter with automatic return

"Type HC - Diverter with automatic return" means 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.

 

3.12 Type HUK1 – Hose union tap incorporating a double check valve

"Type HUK1 - Hose union tap incorporating a double check valve" means a hose union tap in which a double check valve has been incorporated into either the inlet or outlet of the tap.

 

3.13 Type LA – Pressurised air inlet valve

An anti-vacuum valve or vacuum breaker, similar to Type DA but suitable for conditions where the water pressure at the outlet of the device under normal conditions of use is greater than atmospheric.

Maximum permissible fluid category against which a Type LA device is accepted as adequate backflow protection:
  • Backflow by back pressure: Not acceptable for protection against back pressure from any fluid category
  • Backflow by back siphonage: Fluid Category 2

 

3.14 Type LB – Pressurised air inlet valve combined with a check valve downstream

A mechanical backflow prevention device comprising a Type LA anti-vacuum valve and a single check valve located downstream.

Maximum permissible fluid category against which a Type LB device is accepted as adequate backflow protection:
  • Backflow by back pressure: Fluid Category 2
  • Backflow by back siphonage: Fluid Category 3

 

3.15 Upstand Backflow Prevention Device

Type A upstand - An upward flowing supply or distributing pipe surmounted by an anti-vacuum valve (Type DA), or an anti-vacuum valve combined with a single check valve (Type DUK1), any part of the outlet of which is located not less than 300mm above the spillover level of an appliance.

Type B upstand - A branch pipe serving an appliance, where the height of any part of the branch connection to the vented distributing pipe is not less than 300 mm above:
  • the spillover level of the appliance; or
  • the highest possible discharge point served by the vented distributing pipe, whichever is the highest.

 

3.16 Verifiable Backflow Prevention Device

An "upstand" means either one of two alternative arrangements of water fittings to prevent backflow by backsiphonage:

Type A upstand - An upward flowing supply or distributing pipe surmounted by an anti-vacuum valve (Type DA), or an anti-vacuum valve combined with a single check valve (Type DUK1), any part of the outlet of which is located not less than 300mm above the spillover level of an appliance.

Type B upstand - A branch pipe serving an appliance, where the height of any part of the branch connection to the vented distributing pipe is not less than 300 mm above:
  • the spillover level of the appliance; or
  • the highest possible discharge point served by the vented distributing pipe, whichever is the highest.