What is a Backflow prevention valve?
A backflow prevention valve prevents flow of water from a connected device back up into the city water system, ensuring the drinking water is safe from contamination. This could happen when the water pressure in the device exceeds the water pressure in the city water network, or if the city water service pressure drops due to maintenance or pipe breakage. Without backflow valves many connected devices could temporarily feed back into the city water pipework, contaminating the city water supply.
There are 3 levels of backflow protection installations:
- Property containment protection. In this situation the backflow protection valve is installed at the property boundary, just downstream of the water meter.
- Zone protection. This protects specific areas in the building or on the property. Examples include large facilities such as hospitals or golf courses with irrigation systems or multi-building residential developments.
- Individual protection. Backflow valves installed at a specific point of potential contamination within a property. An example would be an underground rainwater tank with an automatic city water top up when low. Generally if a single device is backflow protected, then zone or property protection would not be required.
How A Backflow Prevention Valve Works
The concept is simple – let water easily run into your property or device from the city mains water network, and prevent water running upstream back into the city water system. The mechanics are a little more complicated and the configuration changes, but regardless of the size of pipe and water flow, the principle is the same.
All backflow prevention valves should have a shutoff valve on the upstream side and downstream side to facilitate testing and maintenance. When the pressure on the upstream / inlet side of your backflow valve exceeds 2 psi, water flows through the sensing line and fills the upper chamber of the valve’s diaphragm. This pressure depresses the spring that closes the release valve. When the pressure exceeds 5psi, the first check valve will open, and the main zone will fill with water. Once filled, the second zone will open, allowing water to pass through. When the inlet shut off valve is closed, the first check valve closes, followed by the second check valve. No backflow is permitted through the system as remaining water in the valve is discarded through the relief valve.
Types of Backflow Valves
Backflow prevention valves come in all shapes and sizes! Here is a small selection of the hundreds of valves or types of valves that we’ve worked on over the years. Can you spot yours?
