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What is Backflow in Plumbing?


Backflow is a plumbing term that is used to describe when water flows in the opposite direction. If backflow were to occur in your home or business, it could cause contamination to your water supply. If left for too long, water can become unsafe to drink or bathe.

Backflow testing is required every 12 months for property owners that have; an irrigation system, fire hose reels, commercial machinery connected to the mains or an underground water tank that has a mains water backup.


How does Backflow work?


There a few causes for backflow to occur:

1. Reduced pressure in the water main.
Water systems are designed so that water flows under pressure to and from properties. However, if this pressure is not maintained, water could be drawn back into the water supply system. Many things can affect water pressure, including; a break in the main, water being pumped from the main supply in a fire, water outlet on the property is higher than the main, and a customer is using water at a high pressure than the pressure supplied by the local council.

2. A cross-connection between the drinking water supply and a contaminated source.
When water pressure drops, it creates a vacuum in the water supply system. Sometimes this allows liquid from a contaminated source back into the drinking water supply. Some incidences where this can occur include; in chemical plants where chemicals come into contact with the water supply, when a hose is left running in a container with chemicals, pipe work that allows recycled water to enter the drinking water supply.

3. A nearby property uses the water supply.
A dangerous chemical could get into the water mains which lead to a nearby property. If this contaminated water is then used, residents of the property could be seriously or fatally injured.

Why do you need backflow valve prevention?


A backflow prevention device allows water to travel in one direction but prevents it from travelling backwards in the opposite direction. Every person’s garden and landscape around them have countless things that can make you sick if you drink them. Irrigation water alone has toxic chemicals (fertilisers, pesticides etc) and animal waste (urine and faeces) all through it. These harmful chemicals and pollutants will contaminate your drinking water if you do not have a backflow prevention device.

If you are on a community water system, the water could flow back up the pipes and poison your neighbours. The valves that turn on and off your water system are not sufficient to stop backflow, the purpose of a backflow preventer is to protect you when these valves inevitably break or leak. Many people think that the water pressure in the water system is enough to keep the water from flowing backwards.

Most of the time this is correct, however, there are times when the water pressure drops in the supply system allowing backflow to occur. If a water company has turned off the water supply to repair or install a new pipe, the pressure will drop, the same thing opens when fire-fighters pump huge amounts of water out of fire hydrants.


Backflow valve


What are the backflow prevention requirements in Queensland?


All local governments are required under state legislation to maintain a program for the registration, maintenance and testing of backflow prevention devices installed in their area. Backflow prevention devices stop the reverse flow of water from what could be a polluted source into the water supply. Backflow prevention devices are fitted on:


Irrigation systems that are connected to mains water supply

Fire hose reels

Commercial or industrial machinery connected to the mains

Water outlets close to pollutants, grease traps or chemicals

Underground water tanks that have mains water backup


Whenever a plumber fits a backflow prevention device, they are required to submit the report to the Backflow Register. Each year your local council will issue an Annual Registration Fee Notice and Testing Reminder Notice to the device owner, reminding them to arrange for their devices to be tested before 31 December. State legislation requires owners to register the device with the local government and have the device inspected or tested by a plumber endorsed for backflow testing.


What backflow device do I need?


Each property is designated a hazard rating (low, medium or high). You will need to consult an accredited backflow prevention plumber to determine your property’s hazard rating and the type of device needed. Low hazard properties should install a non-testable backflow prevention containment. Medium hazard properties must install a testable double-check valve assembly. High hazard properties must install a registered break tank, reduced pressure zone or registered air gap. If your property is deemed as a medium or high hazard you will have three months to install the device.


Why do you need a backflow valve replaced


As a general rule of thumb when it comes to deciding to replace or repair a backflow device – if the repair cost exceeds 50% of the cost to replace the device, the best and most economical option is to replace it. Today, there are different materials that backflow valves are manufactured in: ferrous metals, non-ferrous metals and non-metallic materials. Non-ferrous materials include stainless steel which has become the preferred material for newer backflow assemblies. There are a few good reasons to make the switch to stainless steel backflow assemblies: they are up to three times lighter than ferrous backflows and easier to install; new valves are typically less expensive than a replacement of the old design; stainless steel will not corrode so there is no need to worry about epoxy chipping.


What are the different types of backflow preventers?


Reduced Pressure Valve (RVP)


For a commercial site (any business property, apartment complex or condominium) an RVP is the industry standard. This backflow preventer provides the highest level of protection and if anything were to go wrong, a commercial property owner is held to a very high standard of liability. Even if you reside in a residential family house, if you plan to use; fertigation, fertiliser, pesticides or apply anything other than pure water in your irrigation you must install and RVP. This includes products that are labelled as ‘organic’, ‘safe’ or ‘natural’ as while they may be safe when dispersed in the air, they will become much more toxic when concentrated in the water. Double Check Valve (DC)

A DC valve simply has two spring-loaded check valves with a shut-off valve on either end. The DC valve is the only backflow preventer that does not have a vent that allows air to enter the lines or to allow water to escape when backflow occurs. A DC valve is the only type of backflow preventer that can be installed in a large vault with unblockage drainage.
Pressure Vacuum Breaker (PVB)

A PVB is generally installed on the mainline leading to the control valves. It must be installed above ground and be 150mm higher than the highest sprinkler head controlled by any of the valves. A PVB backflow preventer may spill water from under the cap when backflow occurs, as such, it should be installed in a location where water spillage would not cause problems.


Who can replace, install or remove a backflow valve?


Only a licensed plumbing contractor can replace, install or remove a backflow device. When a backflow prevention device is replaced, removed or installed it is the responsibility of the licensed plumbing contractor to submit the correct form to the Queensland Building and Construction Commission.



RPZ Valve


How much does a backflow valve cost?


The cost of a backflow valve differs drastically for each situation. Depending on how many valves you need, your hazard rating and what surrounds your area, the price will fluctuate. As a general rule of thumb backflow preventers fall into the following order, from most expensive to least expensive:


$$$ Reduced pressure valve

$$ Double check valve

$ Pressure vacuum breaker


What is an RPZ Valve?


A reduced pressure zone valve (RPZ) protects water supplies from becoming contaminated or polluted. This specific device is designed to be installed on safe drinking water lines to protect from backflow and potential contamination of the supply. An RPZ valve provides protection where a potential health hazard exists.


What is an RPZ Valve test?


An RPZ test is required to be conducted annually, it tests for backflow and ensures the device is in good working order. Only a licensed plumber can carry out an RPZ valve test, once the test is completed he or she will send the correct paperwork through to your local government.


What is the difference between an RPZ and a DC valve?


RPZ (reduce pressure zone) and DC (double check) valves differ in that RPZ valves are preferred for higher hazard zones whereas DC valves are preferred for lower hazard zones.

Is your backflow prevention device in proper working order? If so, you and the people you live with will be drinking and bathing in clean water with no contaminants. However, if it is not working properly, contamination will occur, it is vital to have regular backflow testing to prevent this.


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