What Is a Backflow Prevention Device?
An introduction to Fluid Categories and Backflow Prevention Types to ensure the safe delivery of wholsome water
| European / UK Classification | Suitable Backflow Prevention Device |
| Fluid Category 5 | Air Gap – AA, AB / Pipe Interrupter – DC |
| Fluid Category 4 | RPZ – BA / Pipe Interrupter – DB |
| Fluid Category 3 | Double Check – ED |
| Fluid Category 2 | Single Check – EB |
| Fluid Category 1 | No device required |
Fluid category 1
Wholesome water supplied by a water undertaker and complying with the requirements of regulations made under section 67 of the Water Industry Act 1991(1).
Fluid category 2
Water in fluid category 1 whose aesthetic quality is impaired owing to–
(a)a change in its temperature, or
(b)the presence of substances or organisms causing a change in its taste, odour or appearance,
including water in a hot water distribution system.
Fluid category 3
Fluid which represents a slight health hazard because of the concentration of substances of low toxicity, including any fluid which contains–
(a)ethylene glycol, copper sulphate solution or similar chemical additives, or
(b)sodium hypochlorite (chloros and common disinfectants).
Fluid category 4
Fluid which represents a significant health hazard because of the concentration of toxic substances, including any fluid which contains–
(a)chemical, carcinogenic substances or pesticides (including insecticides and herbicides), or
(b)environmental organisms of potential health significance.
Fluid category 5
Fluid representing a serious health hazard because of the concentration of pathogenic organisms, radioactive or very toxic substances, including any fluid which contains–
(a)faecal material or other human waste;
(b)butchery or other animal waste; or
(c)pathogens from any other source.
Backflow Prevention Device
Type BA – Verifiable backflow preventer with reduced pressure zone
Type CA – Non-verifiable disconnector with different pressure zones
Type DA – Anti-vacuum valve (or vacuum breaker)
Type DB – Pipe interrupter with atmospheric vent and moving element
Type DUK1 – Anti-vacuum valve combined with a single check valve
Type EA – Verifiable single check valve
Type EB – Non-verifiable single check valve
Type EC – Verifiable double check valve
Type ED – Non-verifiable double check valve
Type HA – Hose union back flow preventer
Type HC – Diverter with automatic return
Type HUK1 – Hose union tap incorporating a double check valve
Type LA – Pressurised air inlet valve
Type LB – Pressurised air inlet valve combined with a check valve downstream
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More Information
A backflow prevention device is a mechanical valve or assembly designed to prevent the undesirable reversal of water flow in a plumbing or water supply system. This helps to protect potable water sources from contamination or pollution caused by backflow, which occurs when water flows in the opposite direction of its intended path due to changes in pressure or other factors.
Backflow can introduce contaminants from non-potable sources, like industrial fluids or wastewater, into the drinking water supply, posing serious health risks. Backflow prevention devices are crucial in safeguarding water quality and public health.
There are several types of backflow prevention devices, including:
Air gap: The simplest form of backflow prevention, an air gap is a physical separation between the potable water supply and a potential source of contamination, ensuring that contaminants cannot reach the potable water.
Atmospheric vacuum breaker (AVB): A mechanical device that uses atmospheric pressure to prevent backflow. It is typically installed on hose bibs or faucets to protect against back-siphonage.
Pressure vacuum breaker (PVB): A device that incorporates both a check valve and an air inlet valve, designed to protect against back-siphonage in low hazard situations.
Double check valve assembly (DCVA): A backflow prevention device consisting of two independent check valves, typically used in low to moderate hazard situations.
Reduced pressure zone (RPZ) assembly: A more complex device with two independent check valves and a pressure relief valve, designed to protect against both back-siphonage and backpressure in moderate to high hazard situations.
Backflow prevention devices are installed in various settings, including residential, commercial, and industrial applications, and are subject to local building codes and regulations. Regular inspection and maintenance are essential to ensure that these devices function properly and continue to protect water supplies.
