The Caleffi vented dual check valve has now been Watermarked and is available from All Valve Industries as well as through leading plumbing stores.
The vented dual check valve is a protection device that prevents backflow of polluted water into the mains water system. This type of backflow can happen due to changes in pressure in the system that causes water to flow backwards.
The vented dual check valve has been approved by a number of authorities (details can be checked with local councils) for use on medium hazard rating applications such as on fully or partially buried rainwater tanks. Vented dual check valves should be installed between the rain water tank and the meter to act as a containment protection device for the mains water service.
Double check valves were traditionally the one solution for medium hazard backflow applications, but the vented dual check valve is more cost effective and does not require an annual test like the double check valve.
Caleffi vented backflow valves were approved for fully or partially buried rainwater tanks in 2006 under AS3500:1 (Section 14), and currently they have been approved by authorities in NSW and SA and are being reviewed by QLD as an acceptable device.