Backflow prevention devices stop water flowing back into our pipes. These devices tend to work using combinations of valves to stop water flowing backward. A backflow preventer is a device that allows the water to flow in only one direction.

A wide choice of devices exists that can be used to prevent back-siphonage and backpressure from adding contaminants into a water supply. The selection of the correct device is based on the degree of hazard (Hazard Rating) posed by the cross-connection. Additional considerations are based upon the piping size, location and the potential need to periodically test the device to ensure correct operation.

Backflow prevention devices have one of the following elements to stop water flowing backward:

• a valve that only lets water go in one direction
• an air gap
• a break tank.

These devices are important as they protect our water quality – and the health of people using it.

There are many types of backflow prevention devices but the most important are:

• Atmospheric Vacuum Breaker – Atmospheric vacuum breakers (AVB) are among the simplest mechanical types of backflow prevention devices and when installed properly, can provide excellent protection against back-siphonage. However, atmospheric vacuum breakers cannot be used to protect against backpressure conditions and are not designed for use in water service installations that are kept under continuous pressure. They are a non-testable device and are only suited for use in Low Hazard installations.
• Pressure Vacuum Breaker – The pressure vacuum breaker (PVB) is an outgrowth of the atmospheric vacuum breaker and evolved in response to the need to have an AVB that can be utilised under constant pressure and that can be tested in-line. This is achieved through spring on top of the disc and float assembly, two added isolation valves, test cocks and an additional first check. PVBs are a testable device. They provide protection against back-siphonage and are suitable for use in Low Hazard or Medium Hazard installations that are under continuous pressure. PVBs do not protect against backpressure.
• Reduced Pressure Zone – Maximum protection is achieved against back-siphonage and backpressure by installing a reduced pressure zone device (RPZD). The RPZD is essentially a modified double check valve with an atmospheric vent capability placed between the two checks and designed such that the zone between the two checks is always kept at least 14 kPa lower than the supply pressure. With these design criteria, the RPZD can provide protection against back-siphonage and backpressure when both the first and second checks become fouled. RPZDs can be used under continuous pressure and are suitable for High Hazard installations. RPZDs are a testable device.
• Double Check Valve – A double check valve (DCV) is essentially two single check valves coupled within one body and furnished with test cocks. The test capability gives this device an advantage over the use of two independent check valves in that it can be readily tested to determine if either or both check valves are inoperative or fouled by debris. Each check is spring-loaded in the closed position and requires approximately 7 kPa to open. The spring-loading provides the ability to “bite” through small debris and still seal; protection feature not prevalent in unloaded swing check valves. DCVs are suitable for use in Medium Hazard installations and can operate under continuous pressure. DCVs can protect against both backpressure and back-siphonage.

Testable backflow prevention devices are those that include features to enable the device to be tested in-situ, i.e. without the need to remove the device. According to AS/NZS 3500.1, the following types of backflow prevention devices are testable Devices:

• Reduced pressure zone device
• Reduced pressure detector assembly
• Double-check valve assembly
• Double-check detector assembly
• Spill-resistant pressure-type vacuum breaker
• Pressure-type vacuum breaker
• Single check valve (testable)
• Single check detector assembly (testable).

Our plumbers are experts in testing and effective backflow prevention solutions to make sure you meet your obligations as a residential or business owner.

It’s our pleasure to answer any inquiry you might have about Backflow Prevention All of Perth’s Services: inspection, installation, repairs, replacement, testing  and maintenance. We’re available 24/7 to take your call, please feel free to contact us at +61 421 004 315.